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acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 1 worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd advanced communications & sensing datasheet 4 the SX8650 is an ultra low power 4-wire resistive touchscreen controller optimized for portable equip ment where power and board-space are at a premium. it incorporates a highly accurate 12-bit adc for da ta conversion and operates from a single 1.65 to 3.7v supply voltage. the SX8650 features a built-in preprocessing algori thm for data measurements, which greatly reduces the host processing overhead and bus activity. this complete touchscreen solution includes four user-selectable operation modes which offer programmability on diff erent configurations such as conversion rate and settling time, thus enable optimization in throughput and power consumption for a wide range of touch sensing appli cations. the touch screen inputs have been specially designe d to provide robust on-chip esd protection of up to 15k v in both hbm and contact discharge, and eliminates the need for external protection devices. the SX8650 supports the fast-mode i2c (400kbit/s) s erial bus data protocol and includes 2 user-selectable sl ave addresses. a custom i2c address is possible on requ est. the SX8650 is offered in two tiny packages: a 3.0 m m x 3.0 mm dfn and a 1.5 mm x 2.0 mm wafer-level chip-s cale package (wlcsp). portable equipment mobile communication devices cell phone, pda, mp3, gps, dsc touch screen monitors extremely low power consumption:23ua@1.8v 8ksps superior on-chip esd protection 15kv hbm (x+,x-,y+,y-) 2kv cdm 25kv air gap discharge 15kv contact discharge 300v mm single 1.65v to 3.7v supply/reference integrated preprocessing block to reduce host loadi ng and bus activity four user programmable operation modes provides flexibility to address different application needs manual, automatic, pen detect, pen trigger high precision 12-bit resolution low noise ratiometric conversion selectable polling or interrupt modes touch pressure measurement 400khz fast-mode i2c interface hardware reset & i2c software reset -40c to 85c operation 12-ld (3.0 mm x 3.0 mm) dfn package 12 ball (1.5 mm x 2.0 mm) wlcsp package pb-free, halogen free, rohs/weee compliant product windows ce 6.0, linux driver support available general description applications block diagram key product features ordering information part number package SX8650icstrt 1 1. 3000 units / reel 12 - ball wlcsp (1.5 mm x 2.0 mm) SX8650iwltrt 1 12 - lead dfn (3.0 mm x 3.0 mm) touch screen interface SX8650 vdd aux x+ y+ x- y- a0 nirq nrst scl sda gnd host control i2c digital filter ref+ ref- adc in out osc por vref
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 2 worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd advanced communications & sensing datasheet
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 2 section page advanced communications & sensing datasheet table of contents 1. general description ............................ ................................................... ................................................... ............... 4 1.1. pin diagram dfn.............................. ................................................... ................................................... ......... 4 1.2. marking information dfn...................... ................................................... ................................................... ..... 4 1.3. pin diagram wlcsp ............................ ................................................... ................................................... ..... 5 1.4. marking information wlcsp .................... ................................................... ................................................... . 5 1.5. pin description.............................. ................................................... ................................................... ............. 6 1.6. simplified block diagram ..................... ................................................... ................................................... ...... 7 2. electrical characteristics ..................... ................................................... ................................................... .............. 8 2.1. absolute maximum ratings ..................... ................................................... ................................................... .. 8 2.2. recommended operating conditions............. ................................................... .............................................. 9 2.3. thermal characteristics ...................... ................................................... ................................................... ....... 9 2.4. electrical specifications .................... ................................................... ................................................... ....... 10 2.5. host interface specifications ................ ................................................... ................................................... ... 12 2.6. host interface timing waveforms.............. ................................................... ................................................. 1 3 2.7. typical operating characteristics ............ ................................................... ................................................... 14 3. functional description ......................... ................................................... ................................................... ............ 16 3.1. general introduction ........................ ................................................... ................................................... ....... 16 3.2. channel pins................................ ................................................... ................................................... ........... 17 3.2.1. x+, x-, y+. y- ............................. ................................................... ................................................... ....... 17 3.2.2. aux ........................................ ................................................... ................................................... ........... 17 3.3. host interface and control pins .............. ................................................... ................................................... . 18 3.3.1. nirq ....................................... ................................................... ................................................... .......... 18 3.3.2. scl ........................................ ................................................... ................................................... ........... 18 3.3.3. sda ........................................ ................................................... ................................................... ........... 18 3.3.4. a0 ......................................... ................................................... ................................................... ............. 19 3.3.5. nrst ....................................... ................................................... ................................................... ......... 19 3.4. power management pins........................ ................................................... ................................................... . 20 3.4.1. vdd........................................ ................................................... ................................................... ........... 20 3.4.2. gnd ........................................ ................................................... ................................................... .......... 20 4. detailed description........................... ................................................... ................................................... .............. 21 4.1. touch screen operation....................... ................................................... ................................................... ... 21 4.2. coordinates measurement...................... ................................................... ................................................... . 22 4.3. pressure measurement......................... ................................................... ................................................... ... 23 4.4. pen detection ................................ ................................................... ................................................... .......... 25 4.5. data processing.............................. ................................................... ................................................... ......... 26 4.6. host interface and control ................... ................................................... ................................................... .... 28 4.6.1. i2c address ................................ ................................................... ................................................... ...... 28 4.6.2. i2c write registers ........................ ................................................... ................................................... ... 29 4.6.3. i2c read registers ......................... ................................................... ................................................... .. 30 4.6.4. i2c host commands .......................... ................................................... .................................................. 31
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 3 section page advanced communications & sensing datasheet table of contents 4.6.5. i2c read channels ......................... ................................................... ................................................... . 32 4.6.6. data channel format ....................... ................................................... ................................................... 33 4.6.7. invalid qualified data ..................... ................................................... ................................................... ... 33 4.7. i2c register map ............................ ................................................... ................................................... ........ 34 4.8. host control writing......................... ................................................... ................................................... ........ 35 4.9. host commands ................................ ................................................... ................................................... ...... 37 4.10. power-up .................................... ................................................... ................................................... ............. 38 4.11. reset....................................... ................................................... ................................................... ................. 38 5. modes of operation ............................ ................................................... ................................................... ............ 39 5.1. manual mode .................................. ................................................... ................................................... ......... 39 5.1.1. convert command ............................ ................................................... .............................................. 39 5.1.2. select command............................. ................................................... ................................................. 4 0 5.2. automatic mode ............................... ................................................... ................................................... ........ 41 5.3. pendet mode .................................. ................................................... ................................................... ...... 42 5.4. pentrig mode ................................. ................................................... ................................................... ...... 42 6. application information ........................ ................................................... ................................................... ............ 44 6.1. acquisition setup ............................ ................................................... ................................................... ......... 44 6.2. channel selection............................ ................................................... ................................................... ........ 44 6.3. noise reduction.............................. ................................................... ................................................... ......... 44 6.3.1. powdly..................................... ................................................... ................................................... ...... 44 6.3.2. setdly ..................................... ................................................... ................................................... ....... 44 6.3.3. aux input .................................. ................................................... ................................................... ........ 45 6.4. channel biasing.............................. ................................................... ................................................... ......... 45 6.5. interrupt generation......................... ................................................... ................................................... ........ 45 6.6. coordinate throughput rate ................... ................................................... ................................................... 46 6.6.1. i2c communication time..................... ................................................... ................................................ 46 6.6.2. conversion time ............................ ................................................... ................................................... ... 46 6.7. application schematic........................ ................................................... ................................................... ...... 48 6.8. application examples......................... ................................................... ................................................... ...... 49 6.8.1. soft keyboard .............................. ................................................... ................................................... ..... 49 6.8.2. game ....................................... ................................................... ................................................... ......... 49 6.8.3. handwriting application.................... ................................................... ................................................... . 50 6.8.4. slider controls............................ ................................................... ................................................... ....... 50 7. packaging information .......................... ................................................... ................................................... ........... 51 7.1. package outline drawing ...................... ................................................... ................................................... .. 51 7.1.1. dfn package ................................ ................................................... ................................................... .... 51 7.1.2. wlcsp package .............................. ................................................... ................................................... 52 7.2. land pattern drawing ......................... ................................................... ................................................... ..... 53 7.2.1. dfn land pattern ........................... ................................................... ................................................... .. 53 7.2.2. wlcsp land pattern ......................... ................................................... .................................................. 54
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 4 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 1. general description 1.1. pin diagram dfn figure 1. pinout diagram, dfn 1.2. marking information dfn figure 2. marking information, dfn on figure 2, yyww is the date code and xxxx is the lot number. 1 2 3 4 5 6 12 11 10 9 8 7 vdd aux x+ y+ x- y- a0 nirq nrst scl sda gnd SX8650 top view 13 8650 yyww xxxx pin 1 identifier
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 5 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 1.3. pin diagram wlcsp figure 3. pinout diagram, wlcsp 1.4. marking information wlcsp figure 4. marking information, wlcsp on figure 4, yyww is the date code and xxxxx is the lot number. SX8650 top view solder bumps on bottom side vdd aux x+ y+ a a0 nirq nrst scl sda gnd b c d 32 1 x- y- 8650 eyww ball a1 identifier
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 6 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 1.5. pin description pin number # name type description dfn wlcsp 1 a2 vdd power input power supply connect to a 0.1uf ca pacitor to gnd 2 a3 x+ analog x+ channel input 3 b3 y+ analog y+ channel input 4 c3 x- analog x- channel input 5 d3 y- analog y- channel input 6 d2 gnd ground ground 7 b1 nirq digital output / open drain output interrupt output, active low. need external pull-up resistor 8 c1 sda digital input / open drain output i2c data inp ut/output 9 d1 scl digital input / open drain output i2c clock, i nput/output 10 c2 nrst digital input / output reset input, active l ow. need external 50k pull-up resistor 11 b2 a0 digital input i2c slave address selection inpu t 12 a1 aux digital input/analog input analog auxiliary i nput or conversion synchronization 13 gnd ground die attach paddle, connect to ground table 1. pin description
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 7 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 1.6. simplified block diagram the SX8650 simplified block diagram is shown in fig ure 5. figure 5. simplified block diagram of the SX8650 touch screen interface SX8650 vdd aux x+ y+ x- y- a0 nirq nrst scl sda gnd control i2c digital filter ref+ ref- adc in out osc por vref
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 8 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 2. electrical characteristics 2.1. absolute maximum ratings stresses above the values listed in absolute maxim um ratings may cause permanent damage to the devic e. this is a stress rating only and functional operati on of the device at these, or any other conditions beyond the recommended operating conditions, is not implied. exposure to absolute m aximum rating conditions for extended periods may a ffect device reliability . (i) tested to tlp (10a) (ii) tested to jedec standard jesd22-a114 (iii) tested to jedec standard jesd78 parameter symbol min. max. unit supply voltage v ddabs -0.5 3.9 v input voltage (non-supply pins) v in -0.5 3.9 v input current (non-supply pins) i in 10 ma operating junction temperature t jct 125 c reflow temperature t re 260 c storage temperature t stor -50 150 c esd hbm (human body model) high esd pins: x+, x-,y+,y- esd hbm1 15 (i) kv 8 (ii) kv all pins except high esd pins: aux,a0,nrst,nirq,sda,scl esd hbm2 2 (ii) kv esd (contact discharge) high esd pins: x+, x-,y+,y- e sd cd 15 kv latchup i lu 100 (iii) ma table 2. absolute maximum ratings
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 9 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 2.2. recommended operating conditions 2.3. thermal characteristics ( i) q ja is calculated from a package in still air, mounted to 3" x 4.5", 4 layer fr4 pcb with thermal vias un der exposed pad (if applicable) per jesd51 standards. parameter symbol min. max unit supply voltage v dd 1.65v 3.7 v ambient temperature range t a -40 85 c table 3. recommended operating conditions parameter symbol min. max unit thermal resistance with dfn package - junction to a mbient (i) q ja 39 c/w thermal resistance with wlcsp package - junction to ambient (i) q ja 65 c/w table 4. thermal characteristics
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 10 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 2.4. electrical specifications all values are valid within the recommended operati ng conditions unless otherwise specified. parameter symbol conditions min. typ max unit current consumption manual i pwd manual (converter stopped, pen detection off, i2c listening, osc stopped) 0.4 0.75 ua pen detect i pndt pen detect mode (converter stopped, pen detection activated, device will generate interrupt upon detection, i2c listening, osc stopped). 0.4 0.75 ua pen trigger i pntr pen trigger mode (converter stopped, pen detection activated, device will start conversion upon pen detection. i2c listening, osc stopped 0.4 0.75 ua automatic i wt automatic (converter stopped, pen detection off, i2c listening, osc and timer on, device is waiting for timer expiry) 1.5 ua operation @8ksps, vdd=1.8v i opl x,y conv. rate=4ksps, n filt =1 powdly=0.5us, setdly=0.5us 23 50 ua operation @42ksps, vdd=3.3v i oph x,y conv. rate=3ksps, n filt =7 powdly=0.5us, setdly=0.5us 105 140 ua digital i/o high-level input voltage v ih 0.7v dd v dd +0.5 v low-level input voltage v il v ss -0.3 0.3v dd v sda / scl hysteresis of schmitt trigger inputs vdd > 2 v vdd < 2 v v hys 0.05v dd 0.1v dd v low-level output voltage v ol i ol =3ma, v dd >2v i ol =3ma, v dd <2v 00 0.4 0.2v dd v input leakage current l i cmos input 1 ua aux input voltage range v iaux 0 v dd v table 5. electrical specifications
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 11 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd input capacitance c x+ ,c x- ,c y+ , c y- 50 pf c aux 5 pf input leakage current i iaux -1 1 ua startup power-up time t por time between rising edge vdd and rising nirq 1 ms adc resolution a res 12 bits offset a off 1 lsb gain error a ge at full scale 0.5 lsb differential nonlinearity a dnl 1 lsb integral nonlinearity a inl 1.5 lsb resistors x+, x-, y+, y- resistance r chn touch pad biasing resistance 5 ohm pen detect resistance r pndt_00 r pndt = 0 100 kohm r pndt_01 r pndt = 1 200 kohm r pndt_10 r pndt = 2 50 kohm r pndt_11 r pndt = 3 25 kohm external components recommendations capacitor between vdd, gnd c vdd type 0402, tolerance +/-50% 0.1 uf parameter symbol conditions min. typ max unit table 5. electrical specifications
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 12 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 2.5. host interface specifications table 6. host interface specifications notes: (i) all timing specifications refer to voltage leve ls (v il , v ih , v ol ) defined in table 5 unless otherwise mentioned. parameter symbol condition min typ max unit i2c timing specifications (i) scl clock frequency f scl 0 400 khz scl low period t low 1.3 us scl high period t high 0.6 us data setup time t su;dat 100 ns data hold time t hd;dat 0 ns repeated start setup time t su;sta 0.6 us start condition hold time t hd;sta 0.6 us stop condition setup time t su;sto 0.6 us bus free time between stop and start t buf 1.3 us data valid time t vd;dat 0.9 us data valid ack time t vd;ack 0.9 us pulse width of spikes that must be suppressed by the input filter t sp 50 ns i2c bus specifications capacitive load on each bus line scl, sda c b 400 pf
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 13 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 2.6. host interface timing waveforms figure 6. i2c start and stop timing figure 7. i2c data timing sda scl t su;sta t hd;sta t su;sto t buf 70% 30% 70% sda scl t low t high t hd;dat t su;dat t sp 30% 70% 30% 70%
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 14 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 2.7. typical operating characteristics at ta= -40c to +85c, vdd=1.7v to 3.7v, powdly=0.5 us, setdly=0.5us, filt=1, resistive touch screen se nsor current not taking in account, unless otherwise noted. current in pen trigger mode 0 100 200 300 400 500 1.5 2 2.5 3 3.5 v dd (v) supply current (na) touch sensor not activated supply current in manual mode vs temperature 0 100 200 300 400 500 600 700 -40 -20 0 20 40 60 80 100 temperature (c) manual mode supply current (na) v dd =3.3v v dd =1.85v supply current vs conversion rate vdd=1.8v - x,y conversion 0 10 20 30 40 50 60 70 80 90 100 0 1 2 3 4 5 conversion rate (kcps) supply current (ua) filt=7 filt=5 filt=3 filt=1 supply current vs conversion rate vdd=1.8v - x,y, z1, z2 conversion 0 10 20 30 40 50 60 70 80 90 100 110 120 130 0 1 2 3 4 5 conversion rate (kcps) supply current (ua) filt=7 filt=5 filt=3 filt=1 supply current vs sample rate 0 100 200 300 400 500 0 1 2 3 4 5 sample rate (kcps) supply current (ua) touch sensor x+ to x- =1000 ohm y+ to y- =1000 ohm v dd =3.3v v dd =2.5v v dd =1.65v
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 15 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd typical operating characteristics (continued) at ta= -40c to +85c, vdd=1.7v to 3.7v, powdly=0.5 us, setdly=0.5us, filt=1, resistive touch screen se nsor current not taking in account, unless otherwise noted. change in adc gain vs. temperature -2 -1 0 1 2 -40 -20 0 20 40 60 80 100 temperature (c) delta from +25c (lsb) change in adc offset vs. temperature -2 -1 0 1 2 -40 -20 0 20 40 60 80 100 temperature (c) delta from +25c (lsb) adc inl @ vdd=3.3v -1 -0.75 -0.5 -0.25 0 0.25 0.5 0.75 1 0 0.5 1 1.5 2 2.5 3 v x+ (v) error (lsb)
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 16 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 3. functional description 3.1. general introduction this section provides an overview of the SX8650 arc hitecture, device pinout and a typical application. the SX8650 is designed for 4-wire resistive touch s creen applications (figure 8).the touch screen or t ouch panel is the resistive sensor and can be activated by either a f inger or stylus. the touch screen coordinates and t ouch pressure are converted into i2c format by the SX8650 for transfe r to the host. figure 8. SX8650 with screen touch screen interface SX8650 vdd aux x+ y+ x- y- a0 nirq nrst scl sda gnd host control i2c digital filter ref+ ref- adc in out osc por vref
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 17 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 3.2. channel pins 3.2.1. x+, x-, y+. y- the SX8650's channel pins (x+, x-, y+, y-) directly connect to standard touch screen x and y resistive layers. the SX8650 separately biases each of these layers and c onverts the resistive values into (x,y) coordinates . the channel pins are protected to vdd and ground. figure 9 shows the simplified diagram of the x+, x- , y+, y- pins. figure 9. simplified diagram of x+, x-, y+, y- pi ns 3.2.2. aux the SX8650 interface includes an aux pin that serve s two functions: an adc input; and a start of conve rsion trigger. when used as an adc, the single ended input range is fro m gnd to vdd, referred to gnd. when the aux input i s configured to start conversions, the aux input can be further con figured as a rising and / or falling edge trigger. the aux is protected to vdd and ground. figure 10 shows a simplified diagram of the aux pin . figure 10. simplified diagram of aux vdd x+ x- y+ y- touch screen interface r chn aux adc control vdd
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 18 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 3.3. host interface and control pins the SX8650 host and control interface consists of: nirq, i2c pins scl and sda, a0, and nrst. 3.3.1. nirq the nirq pin is an active low, open drain output to facilitate interfacing to different supply voltage s and thus requires an external pull-up resistor (1-10 kohm). the nirq pin does not have protection to vdd. the nirq function is designed to provide an interru pt to the host processor. interrupts may occur when a pen is detected, or when channel data is available. figure 11 shows a simplified diagram of the nirq pi n. figure 11. simplified diagram of nirq 3.3.2. scl the scl pin is a high-impedance input and open-drai n output pin. the scl pin does not have protection to vdd to conform to i2c slave specifications. an external pu ll-up resistor (1-10 kohm) is required. figure 12 shows the simplified diagram of the scl p in. figure 12. simplified diagram of scl 3.3.3. sda sda is an i/o pin. it can be used as an open-drain output (with external pull-up resistor) or as an in put. an external pull-up resistor (1-10 kohm) is required. the sda i/o pin does not have protection to vdd to conform to i2c slave specifications. figure 13 shows a simplified diagram of the sda pin . nirq control host vdd irq scl host vdd in out scl i2c
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 19 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd figure 13. simplified diagram of sda 3.3.4. a0 the a0 pin is connected to the i2c address select c ontrol circuitry and is used to modify the device i 2c address. the a0 pin is protected to ground. figure 14 shows a simplified diagram of the a0 pin. figure 14. simplified diagram of a0 3.3.5. nrst the nrst pin is an active low input that provides a hardware reset of the SX8650's control circuitry. the nrst pin is protected ground to enable interfac ing with devices at a different supply voltages. figure 15 shows a simplified diagram of the nrst pi n. figure 15. simplified diagram of nrst sda host vdd in out sda i2c a0 i2c nrst control host vdd
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 20 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 3.4. power management pins the SX8650's power management input consists of the following power and ground pins. 3.4.1. vdd the vdd is a power pin and is the power supply for the SX8650. the vdd has esd protection to ground. figure 16 shows a simplified diagram of the vdd pin . figure 16. simplified diagram of vdd 3.4.2. gnd the SX8650 has one power management ground pin, gnd 1 . the gnd has esd protection to vdd. figure 17 shows a simplified diagram of the gnd pin . figure 17. simplified diagram of gnd 1. the die attach paddle on dfn is also connected to gnd vdd vdd gnd vdd
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 21 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 4. detailed description 4.1. touch screen operation a resistive touch screen consists of two (resistive ) conductive sheets separated by an insulator when not pressed. each sheet is connected through 2 electrodes at the bord er of the sheet (figure 18). when a pressure is app lied on the top sheet, a connection with the lower sheet is establi shed. figure 19 shows how the y coordinate can be m easured. the electrode plates are connected through terminals x+ , x- and y+, y- to an analog to digital converter ( adc) and a reference voltage. the resistance between the terminals x+ an d x- is defined by rxtot. rxtot will be split in 2 resistors, r1 and r2, in case the screen is touched. the resistance between the terminals y+ and y- is represented by r3 and r4 . the connection between the top and bottom sheet is represented by the touch resistance (r t ). figure 18. touch screen figure 19. touch screen operation ordinate measur ement (y) x- y+ y- x+ top conductive sheet bottom conductive sheet electrodes electrodes x- x+ y- y+ r3 r4 r2 r1 + - adc ypos vref + - r t
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 22 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 4.2. coordinates measurement the top resistive sheet (y) is biased with a voltag e source. resistors r3 and r4 determine a voltage d ivider proportional to the y position of the contact point. since the conv erter has a high input impedance, no current flows through r1 so that the voltage x+ at the converter input is given by the v oltage divider created by r3 and r4. the x coordinate is measured in a similar fashion w ith the bottom resistive sheet (x) biased to create a voltage divider by r1 and r2, while the voltage on the top sheet is me asured through r3. figure 20 shows the coordinates measurement setup. the resistance r t is the resistance obtained when a pressure is appl ied on the screen. r t is created by the contact area of the x and y resistive sheet and varies with the applied pressure. figure 20. ordinate (y) and abscissa (x) coordina tes measurement setup the x and y position are found by: x- x+ r2 r1 vref + - r t y- y+ r4 r3 ypos x- x+ r2 r1 vref + - r t y- y+ r4 r3 xpos xpos 4095 r 2 r 1 r 2 + -------------------- = ypos 4095 r 4 r 3 r 4 + -------------------- =
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 23 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 4.3. pressure measurement the pressure measurement consists of two additional setups: z1 and z2 (see figure 21). figure 21. z1 and z2 pressure measurement setup the corresponding equations for the pressure: the x and y total sheet resistance (rxtot, rytot) a re known from the touch screen supplier. r4 is proportional to the y coordinate. the r4 valu e is given by the total y plate resistance multipli ed by the fraction of the y position over the full coordinate range. x- x+ r2 r1 r t y- y+ r4 r3 z1 x- x+ r2 r1 vref + - y- y+ r4 r3 z2 vref + - r t z 1 4095 r 4 r 1 r 4 r t + + --------------------------------- = z 2 4095 r 4 rt + r 1 r 4 r t + + --------------------------------- = rxtot r 1 r 2 + = rytot r 3 r 4 + =
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 24 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd by re-arranging z1 and z2 one obtains which results in: the touch resistance calculation above requires thr ee channel measurements (ypos, z2 and z1) and one s pecification data (rytot). an alternative calculation method is using xpos, yp os, one z channel and both rxtot and rytot shown in the next calculations. r1 is inverse proportional to the x coordinate. substituting r1 and r4 into z1 and rearranging term s gives: r 4 rytot ypos 4095 ------------ = r t r 4 z 2 z 1 ----- 1 C = r t rytot ypos 4095 ------------ z 2 z 1 ----- 1 C = r 1 rxtot 1 xpos 4095 ------------- C = r t rytot y pos 4095 ------------------------------- 4095 z 1 ------------ 1 C rxtot 1 xpos 4095 ------------- C C =
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 25 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 4.4. pen detection if the touchscreen is powered between x+ and y- thr ough a resistor r pndt , no current will flow so long as pressure is not applied to the surface (see figure 22). node x+ wil l remain at the voltage reference voltage. when som e pressure is applied, a current path is created and brings x+ to the level defined by the resistive divider determi ned by r pndt and the sum of r1, r t and r4. the x+ level is detected by a comparator followed b y a s-r latch. r pndt should be set to a value greater than 7x(rxtot + rytot). the pen detection will set the penirq bit of the i2 c status register and will activate (low) the nirq pin of the SX8650. the penirq bit will be cleared and the nirq will be de-asserted as soon as the host reads the i2c stat us register. figure 22. pen detection the resistor r pndt can be configured to 4 different values (see table 9) to accommodate different screen resistive value s. x- x+ r2 r1 vref + - r t y- y+ r4 r3 nirq r pndt s r q q nirq
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 26 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 4.5. data processing the SX8650 offers 4 types of data processing which allows the user to make trade-offs between data thr oughput, power consumption and noise rejection. the parameter filt is used to select the filter ord er n filt as seen in figure 7. the noise rejection will be i mproved with a high order to the detriment of the power consumptio n. the effective coordinate throughput will remain the same for all filter configurations as the adc will be enabled more ofte n. for very high coordinate throughput rates the fi lter needs to be set to filt=0 (see table 7). table 7. filter order figure 23 shows the SX8650 configuration (filt = 0) in which the adc output samples, s n are sent directly to the i2c interface. the filt parameter can be setup through the i2c registers . figure 23. data processing, filt = 0 in the case of filt=1 three output samples of the a dc are averaged and the result is sent to the i2c. figure 24. data processing, filt = 1 filt n filt 0 1 1 3 2 5 3 7 adc s n ,s n-1 ,s n-2 ,.... i2c = c n ,c n-1 ,c n-2 ,.... adc s n ,s n-1 ,s n-2 i2c = - 2 0 3 1 i i n s c n
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 27 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd for filt=2 the averaging is done on five samples . figure 25. data processing, filt = 2 the filt=3 will re-arrange seven samples out of the adc in an ascending order and average the three ce nter samples. figure 26 shows an example of the ordering and aver aging. . figure 26. data processing, filt = 3 adc s n ,s n-1 ,....,s n-4 i2c = - 4 0 5 1 i i n s c n adc s n ,s n-1 ,....,s n-6 i2c = - 2 0 3 1 i i n a sort s n-2 s n-4 s n-5 min max = a n-2 = a n-1 = a n s n-1 s n-6 s n s n-3 c n
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 28 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 4.6. host interface and control the host interface consists of i2c (scl and sda) an d the nirq, a0, nrst signals. the i2c implemented on the SX8650 is compliant with : - standard mode (100 kbit/s) & fast mode (400 kbit/ s) - slave mode - 7 bit slave address 4.6.1. i2c address pin a0 defines the lsb of the i2c address. it is sh own on figure 27. . figure 27. i2c slave address upon request of the customer, a custom i2c address can be burned in the nvm. the host uses the i2c to read and write data and co mmands to the configuration and status registers. d uring a conversion, the i2c clock can be stretched until the end of the processing. channel data read is done by i2c throughput optimiz ed formats. the supported i2c access formats are described in t he next sections: - i2c write registers - i2c read registers - i2c host commands - i2c read channels 1 0 0 1 0 0 0 with pin a0 connected to ground SX8650 slave address(7:1) = 1 0 0 1 0 0 1 with pin a0 connected to vdd
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 29 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 4.6.2. i2c write registers the format for i2c write is given in figure 28. after the start condition [s], the SX8650 slave add ress (sa) is sent, followed by an eighth bit (w=0 ) indicating a write. the SX8650 then acknowledges [a] that it is being a ddressed, and the host sends 8-bit command and regi ster address consisting of the command bits 000 followed by th e SX8650 register address (ra). the SX8650 acknowledges [a] and the host sends the appropriate 8-bit data byte (wd0) to be written. again the SX8650 acknowledges [a]. in case the host needs to write more data, a succee ding 8-bit data byte will follow (wd1), acknowledge d by the slave [a]. this sequence will be repeated until the host termi nates the transfer with the stop condition [p]. figure 28. i2c write register the register address increments automatically when successive register data (wd1...wdn) is supplied by the host. this automatic increment can be used for the first 4 reg ister addresses (see table 8). the correct sampling of the screen by the SX8650 an d the host i2c bus traffic are events that might oc cur simultaneously. the SX8650 will synchronize these events by the use of clock stretching if that is required. the stret ching occurs directly after the last received command bit (see figure 28) . s sa w cr a a wd0 a wd1 a wdn a p optional optional s: start condition sa: SX8650 slave address(7:1) w: '0' a: acknowledge cr: '000' + register address(4:0) wdn: write data byte(7:0), 0...n p: stop condition from host to SX8650 from SX8650 to host clock stretching
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 30 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 4.6.3. i2c read registers the format for incremental i2c read for registers i s given in figure 29. the read has to start with a write of the read address. after the start condition [s], the SX8650 slave add ress (sa) is sent, followed by an eighth bit (w=0 ) indicating a write. the SX8650 then acknowledges [a] that it is being a ddressed, and the host responds with a 8-bit cr dat a consisting of 010 followed by the register address (ra). the sx 8650 responds with an acknowledge [a] and the host sends the repeated start condition [sr]. once again, the sx86 50 slave address (sa) is sent, followed by an eight h bit (r=1) indicating a read. the SX8650 responds with an acknowledge [a] and the read data byte (rd0). if the host needs to read mo re data it will acknowledge [a] and the SX8650 will send the next r ead byte (rd1). this sequence can be repeated until the host terminates with a nack [n] followed by a stop [p]. figure 29. i2c read registers the i2c read register format of figure 29 is mainta ined until the stop condition. after the stop condi tion the SX8650 is performing succeeding reads by the compact read for mat of the i2c read channels described in the next section. no clock stretching will occur for the i2c read reg isters. w cr a s sa a sr sa r a rd0 a rd1 a rdn n p from host to SX8650 from SX8650 to host optional s: start condition sr: repeated start condition sa: SX8650 slave address(7:1) w: '0' r: '1' a: acknowledge n: not acknowledge (terminating read stream) cr: '010' + register address(4:0) rdn: read data byte(7:0), 0...n p: stop condition
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 31 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 4.6.4. i2c host commands the format for i2c commands is given in figure 30. after the start condition [s], the SX8650 slave add ress (sa) is sent, followed by an eighth bit (w=0 ) indicating a write. the SX8650 then acknowledges [a] that it is being a ddressed, and the host responds with an 8-bit data consisting of a 1 + command(6:0). the SX8650 acknowledges [a] and the host sends a stop [p]. the exact definition of command(6:0) can be found i n section [4.9] figure 30. i2c host command the sampling of the screen by the SX8650 and the ho st i2c bus traffic are events that might occur simu ltaneously. the SX8650 will synchronize these events by the use of clock stretching if that is required. the stretchin g occurs directly after the last received command bit (see figure 30). s sa w cr a a p s: start condition sa: SX8650 slave address(7:1) w: '0' a: acknowledge cr: '1' + command(6:0) p: stop condition from host to SX8650 from SX8650 to host clock stretching
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 32 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 4.6.5. i2c read channels the host is able to read the channels with a high t hroughput, by the format shown in figure 31. after the start condition [s], the SX8650 slave add ress (sa) is sent, followed by an eighth bit (r=1 ) indicating a read. the SX8650 responds with an acknowledge [a] and the rea d data byte (rd0). the host sends an acknowledge [a ] and the SX8650 responds with the read data byte (rd1). if t he host needs to read more data, it will acknowledg e [a] and the SX8650 will send the next read bytes. this sequence can be repeated until the host terminates with a n ack [n] followed by a stop [p]. the channel data that can be read is defined by the last conversion sequence. a maximum number of 10 data bytes is passed when al l channels (x, y, z1, z2 and aux) are activated in the i2cregchanmsk. the channel data is sent with the following order: x, y, z1, z2, aux. the first byte of the data conta ins the channel information as shown in figure 32. typical applications require only x and y coordinat es, thus only 4 bytes of data will be read. figure 31. i2c read channels the sampling of the screen by the SX8650 and the ho st i2c bus traffic are events that might occur simu ltaneously. the SX8650 will synchronize these events by the use of clock stretching if that is required. the stretchin g occurs directly after the address and read bit have been sent for the i2c read channels command (see figure 31). s sa r a n s: start condition sa: SX8650 slave address(7:1) r: '1' a: acknowledge n: not acknowledge (terminating read stream) rdn: read data byte(7:0), 0...n p: stop condition from host to SX8650 from SX8650 to host rd0 a rd1 p channel (i+1) rdn-1 a rdn a channel (i) clock stretching
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 33 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 4.6.6. data channel format channel data is coded on 16 bits as shown in figure 32 figure 32. data channel format the 3 bits chan(2:0) are defined in table 12 and sh ow which channel data is referenced. the channel da ta d(11:0) is of unsigned format and corresponds to a value between 0 and 4095. 4.6.7. invalid qualified data the SX8650 will return 0xffff data in case of inval id qualified data. this occurs: - when the SX8650 converted channels and the host c hannel readings do not correspond. e.g. the host co nverts x and y and the host tries to read x, y and z1 and z2. - when a conversion is done without a pen being det ected. c h a n (2:0) r d 0 d (11:8) d (7:0) r d 1 0
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 34 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 4.7. i2c register map the details of the registers are described in the n ext sections. i2c register address ra(4:0) register description 0 0000 i2cregctrl0 write, read 0 0001 i2cregctrl1 write, read 0 0010 i2cregctrl2 write, read 0 0100 i2cregchanmsk write, read 0 0101 i2cregstat read 1 1111 i2cregsoftreset write table 8. i2c register address
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 35 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 4.8. host control writing the host control writing allows the host to change SX8650 settings. the control data goes from the hos t towards the SX8650 and may be read back for verification. register bits default description i2cregctrl0 7:4 0000 rate set rate in coordinates per sec (cps) ( 20%) if rate equals zero then manual mode. if rate is larger than zero then automatic mode 0000: timer disabled -manual mode 0001: 10 cps 0010: 20 cps 0011: 40 cps 0100: 60 cps 0101: 80 cps 0110: 100 cps 0111: 200 cps 1000: 300 cps 1001: 400 cps 1010: 500 cps 1011: 1k cps 1100: 2k cps 1101: 3k cps 1110: 4k cps 1111: 5k cps 3:0 0000 powdly settling time ( 10%): the channel will be biased f or a time of powdly before each channel conversion 0000: immediate (0.5 us) 0001: 1.1 us 0010: 2.2 us 0011: 4.4 us 0100: 8.9 us 0101: 17.8 us 0110: 35.5 us 0111: 71.0 us 1000: 0.14 ms 1001: 0.28 ms 1010: 0.57 ms 1011: 1.14 ms 1100: 2.27 ms 1101: 4.55 ms 1110: 9.09 ms 1111: 18.19 ms i2cregctrl1 7:6 00 auxaqc 00: aux is used as an analog input 01: on rising aux edge, wait powdly and start acquisition 10: on falling aux edge, wait powdly and start acquisition 11: on rising and falling aux edges, wait powdly and start acquisition the aux trigger requires the manual mode. 5 1 condirq enable conditional interrupts 0: interrupt always generated at end of conversion cycle. if no pen is detected the data is set to invalid qualified. 1: interrupt generated when pen detect is successfu l 4 0 reserved 3:2 00 rpdnt select the pen detect resistor 00: 100 kohm 01: 200 kohm 10: 50 kohm 11: 25 kohm 1:0 00 filt digital filter control 00: disable 01: 3 sample averaging 10: 5 sample averaging 11: 7 sample acquisition, sort, average 3 middle sa mples table 9. i2c registers
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 36 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd i2cregctrl2 7:4 0 reserved 3:0 0000 setdly settling time while filtering ( 10%) when filtering is enabled, the channel will initial ly bias for a time of powdly for the first conversion, and for a time of setdly for each subsequent conversion in a filter set. 0000: immediate (0.5 us) 0001: 1.1 us 0010: 2.2 us 0011: 4.4 us 0100: 8.9 us 0101: 17.8 us 0110: 35.5 us 0111: 71.0 us 1000: 0.14 ms 1001: 0.28 ms 1010: 0.57 ms 1011: 1.14 ms 1100: 2.27 ms 1101: 4.55 ms 1110: 9.09 ms 1111: 18.19 ms i2cregchanmsk 7 1 xconv 0: no sample 1: sample, report x channel 6 1 yconv 0: no sample 1: sample, report y channel 5 0 z1conv 0: no sample 1: sample, report z1 channel 4 0 z2conv 0: no sample 1:sample, report z2 channel 3 0 auxconv 0: no sample 1: sample, report aux channel 0 0 reserved 0 0 reserved 0 0 reserved i2cregstat the host status reading allows the host to read the status of the SX8650. the data goes from the sx865 0 towards the host. host writing to this register is ignored. 7 0 convirq 0: no irq pending 1: end of conversion sequence irq pending irq is cleared by the i2c channel reading 6 0 penirq operational in pen detect mode 0: no irq pending 1: pen detected irq pending irq is cleared by the i2c status reading 5:0 000000 reserved i2cregsoftreset 7:0 0x00 if the host writes the value 0xde to this re gister, then the SX8650 will be reset. any other data will not affect the SX8650 register bits default description table 9. i2c registers
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 37 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 4.9. host commands the host can write to and read from registers of th e SX8650 by the write and read commands as defined in table 10. .the host can issue commands to change the operatio n mode or perform manual actions as defined in tabl e 11. the channels are defined as in table 12. w/r command name cr(7:0) function 7 6 5 4 3 2 1 0 write(ra) 0 0 0 ra(4:0) write register (see table 8 for ra) read(ra) 0 1 0 ra(4:0) read register (see table 8 for ra ) table 10. i2c w/r commands command name cr(7:0) function 7 6 5 4 3 2 1 0 select(chan) 1 0 0 0 x chan(2:0) bias channel (see table 1 2 for chan) convert(chan) 1 0 0 1 x chan(2:0) bias channel (see table 12 for chan) wait powdly settling time run conversion manauto 1 0 1 1 x x x x enter manual or automatic mode. pendet 1 1 0 0 x x x x enter pen detect mode. pentrg 1 1 1 0 x x x x enter pen trigger mode. table 11. i2c commands channel chan(2:0) function 2 1 0 x 0 0 0 x channel y 0 0 1 y channel z1 0 1 0 first channel for pressure measurement z2 0 1 1 second channel for pressure measurement aux 1 0 0 auxiliary channel reserved 1 0 1 reserved 1 1 0 seq 1 1 1 channel sequentially selected from i2cregchanmsk register, (see table 8) table 12. channel definition
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 38 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 4.10. power-up the nirq pin is kept low during SX8650 power-up. during power-up, the SX8650 is not accessible and i 2c communications are ignored. as soon as nirq rises, the SX8650 is ready for i2c communication. figure 33. power-up, nirq 4.11. reset the por of the SX8650 will reset all registers and states of the SX8650 at power-up. additionally the host can reset the SX8650 by asser ting the nrst pin (active low) and via the i2c bus. if nrst is driven low, then nirq will be driven low by the SX8650. when nrst is released (or set to hi gh) then nirq will be released by the SX8650. the circuit has also a soft reset capability. when writing the code 0xde to the register i2cregsoftres et, the circuit will be reset. voltage time voltage time vdd nirq t por vdd/2
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 39 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 5. modes of operation the SX8650 has four operation modes that are config ured using the i2c commands as defined in table 11 and table 9. these 4 modes are: - manual (command manauto and rate=0), - automatic (command manauto and rate>0), - pen detect (command pendet), - pen trigger mode (command pentrg). at startup the SX8650 is set in manual mode. in the manual mode the SX8650 is entirely stopped e xcept for the i2c peripheral which accepts host com mands. this mode requires rate equal to be zero (rate = 0, see table 9). in the automatic mode the SX8650 will sequence auto matic channel conversions. this mode requires rate to be larger than zero (rate > 0, see table 9). in the pendet mode the pen detection is activated. the SX8650 will generate an interrupt (nirq) upon p en detection and set the penirq bit in the i2c status register. to q uit the pendet mode the host needs to configure the manual mode. in the pentrg mode the pen detection is activated a nd a channel conversion will start after the detect ion of a pen. the SX8650 will generate an interrupt (nirq) upon pen d etection and set the convirq bit in the i2c status register. to quit the pentrig mode the host needs to configure the ma nual mode. the pentrg mode offers the best compromi se between power consumption and coordinate throughput . 5.1. manual mode in manual mode (rate=0) single actions are triggere d by i2c commands. when a command is received, the SX8650 executes the associated task and waits for the next command. it is up to the host to sequence all acti ons such as: select an input channel, wait for a settling time, start conv ersion and read the result. the commands used in ma nual mode are typically select and/or convert as defined in table 10. the convert command should only be used with condirq=0. if the SX8650 is not ready to execute the next comm and, clock starching occurs. various timing diagram s show the operating sequence for examples of the manual mode. the i2c and the nirq are describing the host interf ace signals. the bias, sample and convert chan nel(s) used on the following drawings are internal SX8650 signals and shown for illustration only. 5.1.1. convert command the convert command will bias the selected channel, wait the time specified by powdly and then convert the selected channel. the converted channel can be one single ch annel or channels in sequence depending on the chan (2:0) parameter. the reading of the channel(s) can be don e over the i2c as described in figure 31. an example host i2c sequence for acquisition of the x channel using the convert command is shown in fi gure 34 and figure 35. the settling time is determined by powdl y the init setup could be a i2c write sequence of: i2cregctrl1=0x00 // no filter, condirq = 0 i2cregchanmsk = 0x80 // acquisition of the x channe l
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 40 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd figure 34. conversion of a channel, no filter figure 35. conversion of a channel, digital filte r enabled, clock starching required 5.1.2. select command the host can define very long settling times by usi ng the select, convert sequence. the host determine s the settling time for each separate channel by the time interval between issuing the select and convert command. th erefore the powdly timing is not applicable and is ignored. as soon as the channel is selected the correspondin g channel will be biased. the settling time is dete rmined by the interval between the host issuing the select and the convert commands. the host can proceed with a read channel command after the convert command. in case the sx86 50 is not ready to convert and filter, the clock of the i2c will be stretched by the SX8650 until data is available and can be read. figure 36 shows an example of i2c sequence using th e select, convert sequence command. for an x-channe l select, issue the command: 0x80, followed with the corresponding convert command: 0x90. the SX8650 wil l make the x-channel data available over the i2c. figure 36. conversion using the select and conver t command init setup convert channel read x position bias channel sample channel convert channel i2c powdly settling time read x init setup convert channel read x position (i2c clock stretched) bias channel sample channel convert channel i2c powdly settling time read x i2c clock stretching init setup select channel read x position bias channel sample channel convert channel i2c read x convert channel host determined settling time
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 41 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd figure 37. single conversion, filtering and inte rrupt signaling in figure 37 the host performs a single conversion and uses the interrupt (nirq) signal to read the av ailable data. the clock stretching is not required and the i2c bus is free for other system traffic. successive reads re quire the same diagram the init setup could be a i2c write sequence of: i2cregctrl1 = 0x23 // interrupt enable, seven sampl es filtering i2cregchanmsk = xconv // acquisition of x 5.2. automatic mode in automatic mode (rate > 0) the SX8650 will automa tically decide when to start acquisition, sequence all the acquisitions and alerts the host if data is available for downlo ad with a nirq. the host will read the channels and the SX8650 will start again with the next conversion cycle. the fastest coordinate rate is obtained if the host reads the channels immediately after the nirq. if the host reads faster than the nirq rate, i2c cl ock stretching occurs or invalid qualified data wil l be returned, see section [4.6.7] to not loose data, the SX8650 will not begin conver sion before the host read the channels. if after th e nirq a delay superior to the sampling period is made by the host to read the channels a slower coordinate rate is o btained. the interrupts will be always generated if the cont rol condirq bit (see table 9) is cleared to 0. in case there is no pen detected on the screen then the coordinate data wil l be qualified as invalid, see section [4.6.7]. thi s result in a regular interrupt stream, as long as the host performs the read channel commands, independent of the screen be ing touched or not. if the control convirq bit (see register i2cregstat table 9) is set to 1 then the interrupts will on ly be generated if the pen detect occurred. this result in a regular interrupt stream, as long as the host performs the read chan nel commands, only when the screen is touched. when the screen is not touched, interrupts does not occur. figure 38 and figure 39 show the automatic-sequenti al mode. after the first sample i2c to make the ini tialization, traffic is reduced as only i2c reads are required. init setup select channel convert channel read x position bias channel sample channel convert channel i2c nirq
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 42 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd figure 38. auto mode, sequential 2-channel conver sion, 3 sample filtering and interrupt signaling, f irst conversion figure 38 shows the very first conversion of 2 chan nels. figure 39 shows the subsequent conversions. i2cregctrl0=0xb8 //1 kcps rate, 140us powdly i2cregctrl1=0x21 // interrupt enable, three samples filtering i2cregchanmsk=0xc0 figure 39. auto mode, sequential 2-channel conve rsion, 3 sample filtering and interrupt signaling, subsequent conversions all succeeding conversions notifies the host by an interrupt signal and the host only needs to issue t he i2c read command. the reads occur at the rate interval. 5.3. pendet mode the pendet mode can be used if the host only needs to know if the screen has been touched or not and t ake from that information further actions. when pen detect circui try is triggered the interrupt signal nirq will be generated and the status register bit penirq will be set. the bit is clear ed by reading the status register i2cregstat. 5.4. pentrig mode the pentrig mode offers the best compromise between power consumption and coordinate throughput. in this mode the SX8650 will wait until a pen is de tected on the screen and then starts the coordinate conversions. the host will be signalled only when the screen is touc hed and coordinates are available. i2c sample channel convert channel powdly powdly x y bias channel setdly setdly setdly setdly nirq init setup read x, y position bias channel sample channel convert channel i2c nirq read x, y position x y rate x
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 43 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd the coordinate rate in pen trigger mode is determin ed by the speed of the host reading the channels an d the conversion times of the channels. the host performs the minimu m number of i2c commands in this mode. figure 40 shows the pentrig mode. in this example, the host waits for the nirq interrupt to make the a cquisition of the x,y data. after the first sample, i2c control traff ic is reduced as only i2c reads are required. figure 40. pen trigger mode init setup read x, y position i2c nirq pen detected read x, y position x,y conversion time x,y conversion time
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 44 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 6. application information this section describes in more detail application o riented data. 6.1. acquisition setup prior to an acquisition, the SX8650 can be setup by writing the control registers. registers are writt en by issuing the register write command. they can be read by issuing the read command. please refer to the section [4.8 ]. if no registers are written, the circuit will start in manual mode. 6.2. channel selection the SX8650 can be setup to start a single channel c onversion or to convert several channels in sequenc e. for a single conversion, the channel to be converted is determin ed from the chan(2:0) field in the command word (de fined in table 12). several channels can be acquired sequentially by se tting the chan(2:0) field to seq. the channels will be sampled in the order defined by register i2cregchanmsk from msb to lsb. if a one is written in a channel mask, the corres ponding channel will be sampled, in the opposite ca se, it is ignored and the next selected channel is chosen. 6.3. noise reduction a noisy environment can decrease the performance of the controller. for example, an lcd display locate d just under the touch screen can adds a lot of noise on the high im pedance a/d converter inputs. 6.3.1. powdly adding a capacitor from the touch screen drivers to ground is a solution to minimize external noise. a low-pass filter created by the capacitor may increase settling time . therefore, use powdly to stretch the acquisition period. powdly can be estimated by the following formula. rtouch is the sum of the panel resistances plus any significant series input resistance, rxtot + rytot + ri. ctouch is the sum of the touch panel capacitance pl us any noise filtering and routing capacitances. 6.3.2. setdly a second method of noise filtering uses an averagin g filter as described in section [4.5] (data proces sing). in this case, the chip will sequence up to 7 conversions on each chan nel. the parameter setdly sets the settling time be tween the consecutive conversions (shown in figure 41). in most applications, setdly can be set to 0. in so me particular applications, where accuracy of 1lsb is required and ctouch is less than 100nf a specific value should b e determined. powdly 10 rtouch ctouch =
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 45 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd figure 41. powdly and setdly timing with filt=2 6.3.3. aux input an alternate conversion trigger method can be used if the host system provides additional digital sign als that indicate noisy or noise-free periods. the SX8650 can be set up to start conversions triggered by the aux pin. a risin g edge, a falling edge or both can trigger the conversion. to enter t his mode, auxacq must be set to a different value t han '00' as defined in table 9. the aux edge will first trigger the bia s delay (powdly). following the programmed delay, t he channel acquisition takes place. 6.4. channel biasing the touch screen surface presents a resistive and c apacitive load, and therefore the screen bias needs to settle before an acquisition takes place. in the manual mode, the ch annels selected are biased when either a select or convert command is received. the channel can be biased for an arbitrary amount o f time by first sending a select command and then a convert command once the settling time requirement is met. the select command can be omitted if the large rang e of powdly settings cover the requirements. in the latter case, the convert command alone is enough to perform an a cquisition. in the sequential mode, multiple channels are sampl ed. this requires programming the powdly field in r egister i2cregctrl0. the selected channel will be powered d uring powdly before a conversion is started. the ch annel bias is automatically removed after the conversion has comp leted. 6.5. interrupt generation an interrupt (nirq) will be generated: - during the power-up phase - after completion of a conversion. convirq (bit [7 ] of i2cregstat) will be set at the same time. - when a pen detect is triggered, the SX8650 being in pen detect mode. penirq (bit [6] of i2cregstat) will be set at the same time. the nirq will be released and then pulled high by t he external pull-up resistor: - when the power-up phase is finished - the host reading all channels that were previousl y converted by the SX8650. convirq, will be cleared at the same time. - the host reading the i2c status register, the sx8 650 being in pen detect mode. penirq, will be clear ed at the same time. powdly setdly start of the conversion time x+ 5 successive conversions
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 46 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd an active nirq (low) needs to be cleared before any new conversions will occur. 6.6. coordinate throughput rate when the chip is not set to automatic mode, the coo rdinate throughput rate depends on the following fa ctors: - the i2c communication time - the conversion time if the SX8650 is set to automatic mode then the rat e settling must not be faster than the raw conversi on rate (rcr). 6.6.1. i2c communication time the time to read the channel data by i2c depends of the mode set and if the clock is stretched or not. the highest throughput will be obtained with a i2c frequency of 400khz and clock stretching when all c hannels are sampled in pentrig mode. the host should react to the nirq interrupt signal as quickly as possible by reading the channel data. 6.6.2. conversion time the maximum possible throughput can be estimated wi th the following equation with: - n filt = {1,3,5,7} based on the order defined for the fil ter filt (see figure 7). - n chan = {1,2,3,4,5} based on the number of channels defi ned in i2cregchanmsk - powdly = 0.5us to 18.19ms, settling time as defin ed in i2cregctrl0 - setdly = 0.5us to 18.19ms, settling time when fil tering as defined in i2cregctrl2 - tosc is the oscillator period (555ns +/- 15%) the coordinate rate (cr) and equivalent coordinate rate (ecr) which give the number of coordinates (x, y, z1, z2) is given below : mode clock stretching t comm (us) manual no t su;sta -t low + (29+18*nchan)*t scl manual yes -t low + (21+18*nchan)*t scl pentrig 1 1. with the pen always down no t su;sta -t low + (9+18*nchan)*t scl pentrig 1 yes -t low + (1+18*nchan)*t scl table 13. rcr kcps ( ) 1000 t conv us ( ) = tconv us ( ) 47 tosc n + chan powdly n filt 1 C ( ) setdly 21 n filt 1 + ( ) tosc + + ( ) = cr kcps ( ) 1000 t us ( ) =
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 47 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd the sample rate (sr) and equivalent sample rate (es r) which give the number of sample per second (x, y , z1, z2) is given below table 14 gives some examples of coordinate rate and sample rate for various setting in pentrig mode. nch [1..5] nfilt [1 3 5 7] powdly [us] setdly [us] tconv [us] tcomm [us] total [us] cr [kcps] ecr [kcps] sr [ksps] esr [ksps] 2.0 1.0 0.5 0.5 51.7 91.2 142.9 7.0 14.0 7.0 14.0 2.0 1.0 2.2 0.5 55.0 91.2 146.2 6.8 13.7 6.8 13.7 2.0 1.0 8.9 0.5 68.3 91.2 159.5 6.3 12.5 6.3 12.5 2.0 1.0 35.5 0.5 121.7 91.2 212.9 4.7 9.4 4.7 9.4 2.0 1.0 280.0 0.5 619.4 91.2 710.6 1.4 2.8 1.4 2.8 2.0 3.0 2.2 0.5 103.9 91.2 195.1 5.1 10.3 15.4 30.8 2.0 3.0 35.5 0.5 170.6 91.2 261.8 3.8 7.6 11.5 22.9 2.0 5.0 2.2 0.5 152.8 91.2 244.0 4.1 8.2 20.5 41.0 2.0 5.0 35.5 0.5 219.4 91.2 310.6 3.2 6.4 16.1 32.2 4.0 7.0 2.2 0.5 377.2 181.2 558.4 1.8 7.2 12.5 50.1 4.0 7.0 35.5 0.5 510.6 181.2 691.8 1.4 5.8 10.1 40.5 4.0 1.0 0.5 0.5 77.2 181.2 258.4 3.9 15.5 3.9 15.5 4.0 1.0 2.2 0.5 83.9 181.2 265.1 3.8 15.1 3.8 15.1 4.0 1.0 35.5 0.5 217.2 181.2 398.4 2.5 10.0 2.5 10.0 4.0 3.0 2.2 0.5 181.7 181.2 362.9 2.8 11.0 8.3 33.1 4.0 3.0 35.5 0.5 315.0 181.2 496.2 2.0 8.1 6.0 24.2 4.0 5.0 2.2 0.5 279.4 181.2 460.6 2.2 8.7 10.9 43.4 4.0 5.0 35.5 0.5 412.8 181.2 594.0 1.7 6.7 8.4 33.7 4.0 7.0 2.2 0.5 377.2 181.2 558.4 1.8 7.2 12.5 50.1 4.0 7.0 35.5 0.5 510.6 181.2 691.8 1.4 5.8 10.1 40.5 table 14. coordinate throughput examples ecr kcps ( ) n chan cr = sr ksps ( ) n filt cr = esr ksps ( ) n chan n filt cr =
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 48 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 6.7. application schematic a typical application schematic is shown in figure 42 figure 42. typical application touch screen interface SX8650 vdd aux x+ y+ x- y- a0 nirq nrst scl sda gnd host control i2c digital filter ref+ ref- adc in out osc por vref
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 49 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 6.8. application examples 6.8.1. soft keyboard figure 43. keyboard a keyboard application can be designed with the hel p of the SX8650. the data are entered by tapping ke ys on the keyboard with a stylus. the SX8650 send the key coo rdinates to the microcontroller which interpret the m as a symbol. when the keyboard is not activated, the chip stays in low power mode to save power. 6.8.2. game figure 44. game many kinds of game can be designed with touchscreen . with its high data throughput and its ability to sense pressure, SX8650 is the perfect controller for this kind of a pplication.
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 50 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 6.8.3. handwriting application figure 45. handwriting application an handwriting application needs a powerful microco ntroller to run recognition algorithms. the SX8650 includes a preprocessing block to reduce host activity. 6.8.4. slider controls figure 46. slider controls every kind of controls such as rotative knob, slide r, button could be emulated with a SX8650 associate d to a touchscreen.
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 51 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 7. packaging information 7.1. package outline drawing 7.1.1. dfn package the 12-lead dfn (3mm x 3mm) package is shown in fig ure 47 figure 47. dfn package outline drawing (laser mark) indicator pin 1 1 n 2 min aaa bbb be l n e1 d1 e a1 a2 a dim millimeters nom dimensions max nom inches min max .114 .118 .122 2.90 3.00 3.10 a1 a2 lxn e1 d1 e/2 bxn d .114 .118 .122 2.90 3.00 3.10 d e e/2 d/2 a notes: controlling dimensions are in millimeters (angles i n degrees). coplanarity applies to the exposed pad as well as t erminals. 2. 1. .003 .006 .042 12 .008 .048 .000 .028 (.008) 0.08 0.20 12 .010 .052 0.15 1.06 .031 .002 0.00 0.70 1.31 0.25 1.21 0.05 0.80 (0.20) .004 0.10 0.45 bsc .018 bsc 0.30 .012 .020 .016 0.40 0.50 aaa c seating plane a bbb c a b b e c .074 .079 .083 1.87 2.02 2.12 0.02 0.75 .001 .030
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 52 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 7.1.2. wlcsp package the wlcsp-w12 package as shown in figure 48 figure 48. wlcsp package outline drawing 0.625 max. 0.10 c 0.08 c 0.05 c a b controlling dimensions are in millimeters notes: 1. a b c a b c index area a1 corner 0.250.10 seating 1 2 3 d 1.50.10 2.00.10 0.50 1.00 0.25 0.50 1.50 12x ?.300.05 plane
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 53 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 7.2. land pattern drawing 7.2.1. dfn land pattern the land pattern of 12-lead dfn (3mm x 3mm) is show n in figure 49. figure 49. dfn land pattern .087 .055 2.20 1.40 .150 .018 .010 .037 3.80 0.25 0.95 0.45 (.112) .075 1.90 (2.85) this land pattern is for reference purposes only. consult your manufacturing group to ensure your company's manufacturing guidelines are met. notes: 2. thermal vias in the land pattern of the exposed pad shall be connected to a system ground plane. functional performance of the device. failure to do so may compromise the thermal and/or 3. inches dimensions g k h xy p z c dim millimeters h k g y z p (c) x controlling dimensions are in millimeters (angles in degrees). 1.
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 54 advanced communications & sensing datasheet worlds lowest power & smallest footprint 4-wire resistive touchscreen controller with 15kv esd 7.2.2. wlcsp land pattern the land pattern of wlcsp is shown on figure 50 figure 50. wlcsp land pattern this land pattern is for reference purposes only. consult your manufacturing group to ensure your notes: 2. company's manufacturing guidelines are met. 1. controlling dimensions are in millimeters 0.50 0.25 1.50 0.50 1.00 12x ?0.325
acs revision v2.15/october 2009 ?2009 semtech corp. SX8650 www.semtech.com page 55 semtech corporation advanced communications & sensi ng products contact information e-mail: sales@semtech.comacsupport@semtech.cominter net: http://www.semtech.com usa 200 flynn road, camarillo, ca 93012-8790. tel: +1 805 498 2111 fax: +1 805 498 3804 far east 12f, no. 89 sec. 5, nanking e. road, taipei, 105, t wn, r.o.c. tel: +886 2 2748 3380 fax: +886 2 2748 3390 europe semtech ltd., units 2 & 3, park court, premier way, abbey park industrial estate, romsey, hampshire, s o51 9dn. tel: +44 (0)1794 527 600 fax: +44 (0)1794 527 601 iso9001 certified advanced communications & sensing datasheet ? semtech 2008 all rights reserved. reproduction in whole or in pa rt is prohibited without the prior written consent of the copyright owner. the information presented in this document does not for m part of any quotation or contract, is believed to be accurate and reliable and may be changed without notice. no liability wil l be accepted by the publisher for any consequence of its use. publication thereof does not convey nor imply any license under patent or other industrial or intellectual propert y rights. semtech assumes no responsibility or liability whatsoever for any f ailure or unexpected operation resulting from misus e, neglect improper installation, repair or improper handling or unusua l physical or electrical stress including, but not limited to, exposure to parameters beyond the specified maximum ratings or operation outside the specified range. semtech products are not designed, intended, author ized or warranted to be suitable for use in life-support applications, devices or systems or ot her critical applications. inclusion of semtech products in such applications is understood to be undertaken solely at the customers own risk. should a customer purchase or use semtech products for any such unauthorized application, th e customer shall indemnify and hold semtech and its officers, employ ees, subsidiaries, affiliates, and distributors har mless against all claims, costs damages and attorney fees which could arise.

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