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[ASAHI KASEI] [AK4180] AK4180 Features: Sampling Frequency: 125kHz(max) Pen Pressure Measurement On-Chip Thermo Sensor Two Auxiliary Analog Inputs Direct Battery Measurement 4-wire I/F On-Chip Voltage Reference(2.5V) 12 bit SAR type A/D Converter Low Power Consumption (250A) Low Voltage Operation (2.7V - 3.6V) Package 16pin TSSOP Touch Screen Controller General Description: The AK4180 is a 4-wire touch screen controller that incorporates a 12-bit 125kHz sampling SAR A/D converter. The AK4180 can detect the pressed screen location by performing two A/D conversions. In addition to location, the AK4180 also measures touchscreen pressure. On-chip VREF can be utilized for two analog auxiliary inputs and battery monitoring, with the ability to measure voltages from 0V to 5V. The AK4180 also has an on-chip temperature sensor. XP DCLK CSN YP DIN XN Control Logic DOUT BUSY YN IN1 Internal VREF(2.5V) VREF IN2 VBAT R1 AIN+ VREF+ VREF- R2 AIN- 12bit ADC (SAR type) PENIRQN PEN INTERRUPT Temp. Sensor VCC GND Block Diagram 1 2003/02 [ASAHI KASEI] [AK4180] Ordering Guide AK4180VT -20C +70C 16pinTSSOP Pin Layout VCC XP YP XN YN GND VBAT IN1 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 DCLK CSN DIN BUSY DOUT PENIRQN IN2 VREF 2 2003/02 [ASAHI KASEI] [AK4180] Pin/Function No. 1 2 Signal Name VCC XP I/O I/O Description Power Supply Touch Screen X+ plate Voltage supply X axis Measurement: Supplies the voltage Y axis Measurement: This pin is used as the input for the A/D converter Pen Pressure Measurement: This pin is the input to the A/D converter at Z1 measurement. Temperature/VBAT/IN1/IN2 Measurement: OPEN state Powerdown State: is pulled up by an internal resistor (typ.20k ohm). Touch Screen Y+ plate Voltage supply Y axis Measurement: Supplies the voltage X axis Measurement: This pin is used as the input for the A/D converter Pen Pressure Measurement: Supplies the voltage. Temperature/VBAT/IN1/IN2 Measurement: OPEN state Powerdown State: OPEN state. Touch Screen X- plate Voltage supply X axis Measurement: Supplies the voltage Y axis Measurement: OPEN state Pen Pressure Measurement: Supplies the voltage. Temperature/VBAT/IN1/IN2 Measurement: OPEN state Powerdown State: OPEN state Touch Screen Y- plate Voltage supply Y axis Measurement: Supplies the voltage X axis Measurement: OPEN state Pen Pressure Measurement: This pin is the input to the A/D converter at Z2 measurement. Temperature/VBAT/IN1/IN2 Measurement: OPEN state Powerdown State: connected to GND. Ground Analog Input for Battery Monitor Auxiliary 1 Analog Input Voltage Reference Input/Output Outputs 2.5V Auxiliary 2 Analog Input Pen Interrupt Output This pin should be pulled up via a 100k-ohm resistor. Serial A/D Data Output Outputs A/D data serially at the falling edge of DCLK. MSB is output at the falling edge of BUSY signal. DOUT is "L" at CSN="L" except that A/D data is output. This pin is Hi-Z state at CSN="H" BUSY Output This pin goes to low at CSN = "L". BUSY signal is "H" only for the period between the falling edge of 8DCLK and the falling edge of 9DCLK. This pin is Hi-Z state at CSN="H" Serial Data Input Inputs 8-bit control command data serially when CSN="L" AK4180 latches at the rising edge of DCLK. Please keep "L" except when issuing commands. Chip Select Input Enables writing to the registers when CSN="L". CSN="H" and DIN="H" force the internal registers to initial value, 00h. (Full Powerdown) External Clock Input 3 YP I/O 4 XN I/O 5 YN I/O 6 7 8 9 10 11 12 GND VBAT IN1 VREF IN2 PENIRQN DOUT I I I/O I O O 13 BUSY O 14 DIN I 15 CSN I 16 DCLK I 3 2003/02 [ASAHI KASEI] [AK4180] Absolute Maximum Ratings GND=0V Parameter Power Supplies Input Current (any pins except for supplies) Input Voltage Touch Panel Drive Current Ambient Temperature (power supplied) Storage Temperature All voltages with respect to ground. Symbol VCC IIN VIN IOUTDRV Ta Tstg Min -0.3 -0.3 -20 -65 max 6.0 10 6.0(VCC+0.3) 50 70 150 Units V mA V mA C C WARNING: Operation at or beyond these limits may result in permanent damage to the device. Normal operation is not guaranteed at these extremes. Recommended Operating Conditions GND=0V Parameter Power Supplies All voltages with respect to ground. Symbol VCC min 2.7 typ 3.3 max 3.6 Units V 4 2003/02 [ASAHI KASEI] [AK4180] Analog Characteristics Ta=-20C to 70C,VCC=2.7V, Vref=2.5V, fs=125kHz, MCLK=16*fs Parameter min typ Max Units ADC for Touch Screen Resolution 12 Bits No Missing Code 10 12 Bits Integral Linearity Error LSB 5 Analog Input Voltage Range 0 Vref V Offset Error 0 20 LSB Gain Error -12 0 LSB Touch Panel Driver 5 X+, Y+, RL=300 5 X-, Y-, RL=300 PSRR 70 dB Reference Output 2.4 2.5 2.55 V Internal Reference Voltage@VCC=3.0V, 20C Load Capacitance 0.1 uF Reference Input Input Voltage Range VCC V Input Impedance 98 196 k Battery Monitor Input Voltage Range 5.0 V Input Impedance (Battery Measure Mode) 10 k Accuracy *) % 3 Temperature Measurement Temperature Range -20 70 V Resolution **) 1.6 C Accuracy ***) 3 C Power Supply Current Normal Mode (Internal VREF OFF) 250 500 A Normal Mode (Internal VREF ON) 520 800 A Full Power Down 0 10 A *) Accuracy is the difference between the output code when 5 volts is input to the VBAT pin and the "ideal" code at 1.25 volts. **) "ideal" value derived from theory **) Accuracy is defined as the difference between the voltage measured by two current sources, and the ideal voltage derived from theory at specific temperatures. 5 2003/02 [ASAHI KASEI] [AK4180] DC Characteristics (Logic I/O) Ta=-20 to 70C,VCC=2.7V to 3.6V Parameter "H" level input voltage "L" level input voltage Input Leakage Current "H" level output voltage (@ Iout = -250uA) "L" level output voltage (@ Iout= 250uA) Tri-state Leakage Current All pins except for XP, YP, XN, YN pins XP, YP, XN, YN pins PENIRQN "L" level output voltage (100K Pull-Up) Symbol VIH VIL IILK VOH VOL IOLK -10 VCC-0.4 -10 -50 VOLP min 0.8xVCC 0.2xVCC 10 0.4 10 50 0.8 V uA V V uA uA V Typ max Units V Switching Characteristics Ta=-20C to 70C, VCC=2.7V to 3.6V Parameter Touch Panel (A/D Converter) Throughput Rate DCLK frequency duty Tracking Time (Rin=600) Conversion Time CSN "" to First DCLK "" CSN "" to BUSY Tri-State Disabled CSN "" to DOUT Tri-State Disabled DCLK High Pulse Width DCLK Low Pulse Width DCLK "" to BUSY "" Data Setup Time Data Valid to DCLK Hold Time Data Access Time after DCLK "" CSN "" to DCLK Ignored CSN "" to BUSY High-Z state CSN "" to DOUT High-Z state Symbol min Typ max 125 fDCLK duty tTRK tCONV t1 t2 t3 t4 t5 t6 t7 t8 t9 t10 t11 t12 10 40 1.5 100 200 200 200 200 200 100 10 200 0 200 200 2000 60 12 Units kHz kHz % us 1/fDCLK ns ns ns ns ns ns ns ns ns ns ns ns 50 CSN t5 t1 DCLK t8 t7 DIN P0 t4 t6 t6 t9 t10 t2 BUSY t11 t3 DOUT D11 D10 D0 t12 AK4180 Timing Diagram 6 2003/02 [ASAHI KASEI] [AK4180] A/D Converter for Touch Screen The AK4180 incorporates a12-bit successive approximation resistor A/D converter for position measurement, temperature, and battery voltage. The architecture is based on capacitive redistribution algorithm, and an internal capacitor array functions as the sample/hold circuit. The A/D converter output is a straight binary format as shown below: Input Voltage Output Code FFF (VREF-1.5LSB)~ VREF FFE (VREF-2.5LSB) ~ (VREF-1.5LSB) ----------------0.5LSB ~ 1.5LSB 001 0 ~ 0.5LSB 000 VREF: (VREF+) - (VREF-) Table 1 Output Code The A/D converter's full scale measurements depend on the input mode. Analog Inputs Analog input is selected via the A2, A1, A0 and SER/ DFR bits in the control register. If the analog inputs are the X or Y-axis, use SER/ DFR = "0", which means differential mode, the full scale (VREF) is the differential voltage between the non-inverting terminal and the inverting terminal of the measured axis (e.g. (XP) - (XN)). Analog non-inverting input to A/D converter is the non-inverting terminal of the non-measured axis while the inverting input is the inverting terminal of the measured axis. If the SER/ DFR bit is set to "1", which means single-ended mode, the full scale of A/D converter (VREF) is the internal reference voltage, or external reference voltage. Note that SER/ DFR bit should be set to "0" if IN2 is selected as analog input; nevertheless, IN2 is actually measured by single-ended mode. Tracking time is the period from the falling edge of 5th DCLK to the falling edge of 8th DCLK after the detection of START bit. the required settling time to charge the internal capacitors depends on the source impedance. If the source impedance, Rin, is 600 ohm, the settling time needs at least 1.5 s (3 tDCLK@2MHz). The maximum throughput of A/D converter is 125kHz. If the source impedance of analog input is larger than 600 ohm, longer tracking time is required. The Position Detection of Touch Screen The selected touch screen position is detected by the voltage measurement of one axis when the voltage is supplied between the two terminals of the other axis. At least two A/D conversions are needed to get the two-dimensional (X/Y axis) position. 7 2003/02 [ASAHI KASEI] [AK4180] ON XP ON XP VREF+ AIN+ VREF+ AIN+ ADC VREFAIN- YP ADC VREFAIN- YP XN XN ON YN ON YN a) X-Position Measurement Differential Mode b) Y-Position Measurement Differential Mode Figure 1 Axis Measurement The differential mode position detection is typically more accurate than the single-ended mode. As the full scale of single-ended mode is fixed to the internal (or external) reference voltage, input voltage may exceed the full-scale reference voltage. This problem does not occur in differential mode. In addition to this, the differential mode is less influenced by power supply voltage variation due to the ratio-metric measurement. However, note that the touch screen driver switch is still ON and the current flows even for the A/D conversion time. On the other hand, the touch screen driver switch is ON only for the tracking time, 3tDCLK. From the power consumption, single-ended mode has more advantage. The Pen Pressure Measurement The touch screen pen pressure can be derived from the measurement of the contact resistor between two plates. The contact resistance depends on the size of the depressed area and the pressure. The area of the spot is proportional to the contact resistance. This resistance (Rtouch) can be calculated using two different methods. The first method uses the total resistance of the X-plate sheet. The resistance, Rtouch, is calculated from the results of three conversions, X-position, Z1-Position, and Z2-Position, using the following formula: Rtouch = (Rxplate) * (Xposition/4096) * [ (Z2/Z1) - 1] The second method uses the resistances of both the X-plate and Y-plate. The resistance, Rtouch, is calculated from the results of three conversions, X-position, Y-Position, and Z1-Position, using the following formula: Rtouch = (Rxplate*Xposition/4096)*[(4096/Z1) - 1] - Ryplate*[1 - (Yposition/4096)] 8 2003/02 [ASAHI KASEI] [AK4180] ON YP ON YP XP VREF+ AIN+ touch VREF+ AIN+ XP touch ADC VREFAIN- ADC VREFAIN- XN XN ON YN ON YN b) Z1-Position Measurement Differential Mode a) Z2-Position Measurement Differential Mode Figure 2 Pen Pressure Measurement Voltage Reference The AK4180 has an internal 2.5V voltage reference. This reference can be turned ON when PD1 = "1", and OFF when PD1 = "0". This reference is used in the single-ended mode for the battery monitoring, temperature measurement, or for auxiliary input. A 0.1F or larger capacitor should be connected for stable operation of the VREF circuit. Setting time depends on this external capacitance, but 400s or longer time is required if the external capacitance is 0.1F. If an external voltage reference is used, PD1 bit should be set to "0". Battery Measurement The AK4180 can measure the battery voltage that is up to 5V directly while the AK4180 operates at 2.7V or 3.3V, etc. The input voltage is internally divided down by 4. Minimum 5s is required as tracking time. If the source impedance is large, more tracking time is required. Internal VREF VBAT R0 R1=7.5K AINR2=2.5K AIN+ ADC PD1 VREF+ VREF- Enable Figure 3 Battery Monitoring 9 2003/02 [ASAHI KASEI] [AK4180] Temperature Measurement Equation <1> describes the forward characteristics of the diode. iD=I0exp(vD/VT) ( VT = kT/q) <1> I0: reverse saturation current q : 1.602189x10-19 (electron charge) k : 1.38054x10-23 (Boltzmann's constant) vD: voltage across diode T: absolute temperature K The diode characteristics is approximately showed As a diode junction voltage is theoretically proportional to the temperature, the ambient temperature can be predicted by knowing this voltage. I Temp. Sensor 82I TEMP0 TEMP0 Figure 4 Temperature Measurement As the AK4180 has two different fixed current circuits and a diode, the temperature can be measured by using two different methods. The first method needs two conversions, but can derive the temperature directly without knowing the voltage at a specific temperature. From equation <1> (iD2 / iD1) = exp{(v(NI) - v(I))/VT} N = (iD2 / iD1) = 82 (ratio of the current) TC = (Vbe * q)/(k * ln N) - 273 Vbe = V(NI) - V(I) TC = 2.63x103 x Vbe - 273 The second method needs only one conversion as the following equation, but requires knowing the junction voltage at the specific temperature. T = (k/q)* vD/ln(iD/I0) <2> 10 2003/02 [ASAHI KASEI] [AK4180] Control Command The control command, 8 bits, provided to the AK4180 via DIN is shown in the following table. This command includes start bit, analog input, resolution, measurement configuration, and power-down mode. The AK4180 latches the serial command at the rising edge of DCLK. D7 S D6 A2 D5 A1 D4 A0 D3 MODE D2 SER/ DFR D1 PD1 D0 PD0 BIT 7 6-4 3 2 3 Name S A2-A0 MODE SER/ DFR PD1-PD0 Function Start Bit. This bit must be "H" because the AK4180 initiates the command recognition Channel Selection Bits. Analog inputs to the A/D converter and the activated driver switches are selected. Please see the following table for the detail. Resolution of A/D converter. "L": 12 bit output "H": 8 bit output Measurement Mode (Single-Ended/Differential) Power-down Mode (reference to " Power-down Control") Control Command A2 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 A1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 A0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 SER/ DFR 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 Status of Driver Switch XP OFF OFF OFF OFF OFF ON OFF OFF OFF OFF OFF ON OFF XN OFF OFF OFF ON ON ON OFF OFF OFF ON ON ON OFF YP OFF ON OFF ON ON OFF OFF OFF ON ON ON OFF OFF YN OFF ON OFF OFF OFF OFF OFF OFF ON OFF OFF OFF OFF ADC input (AIN) AIN+ TEMP0 XP VBAT XP(Z1) YN(Z2) YP IN1 TEMP1 XP XP(Z1) YN(Z2) YP IN2 AINGND GND GND GND GND GND GND GND YN XN XN XN GND Reference Voltage (VREF) VREF+ VREFVREF VREF VREF VREF VREF VREF VREF VREF YP YP YP XP VREF GND GND GND GND GND GND GND GND YN XN XN XN GND Note TEMP0 Y-axis Battery Monitor Z1 (Pen Pressure) Z2 (Pen Pressure) X-axis IN1 TEMP1 NA Y-axis NA Z1 (Pen Pressure) Z2 (Pen Pressure) IN1 TEMP1 NA *) Note that IN2 auxiliary input is measured by single-ended mode although SER/ DFR bit is "0". Table 2 Control Command List 11 2003/02 [ASAHI KASEI] [AK4180] Power-down Control Power-down is controlled by two bits, PD0 bit and PD1 bit. The power-down state of internal voltage reference is controlled by PD1 bit, and is updated at the rising edge of 7th DCLK with CSN="L". The power-down state of A/D converter, and touch screen driver switches is controlled by PD0 bit, and is updated at the rising edge of 8th DCLK with CSN="L". If PD0 bit is set to "1", the state of the driver switches is maintained until the 5th DCLK of the next conversion if CSN is "L". If CSN is "H", all driver switches except for YN switch switches are turned off and are open states. Only YN driver switch is turned ON and YN pin is forced to the ground in this case. PD1 0 PD0 0 PENIRQN Enabled Function Auto Power-down Mode. A/D converter is automatically powered up at the initiation of the conversion, and goes to powerdown state automatically at the end of the conversion. And the AK4180 is always powered down at this mode if CSN="H". All touch screen driver switches except for YN switch are turned off and relative pins are open state. Only YN driver switch is turned ON and YN pin is forced to the ground in this case. PEN interrupt function is enabled except for the tracking time and conversion time even CSN="L". Please see " PEN Interrupt" for the detail. The internal voltage reference is always power-down state. ADC ON Mode A/D converter is always powered up while CSN = "L". The internal voltage reference is always power-down state. if X-axis or Y axis is selected as analog input, touch screen driver switches are always turned ON and the current flows through the touch plate if CSN="L". This is effective if more settling time for is required to suppress the electrical bouncing of touch plate. VREF ON Mode The internal voltage reference is always powered up regardless of CSN state. ADC is auto powerdown mode. PEN interrupt function is enabled at all the period except for the period from the 5DCLK to 20DCLK regardless of CSN state. ADC and VREF ON Mode A/D converter and the internal voltage reference is power-up state PEN interrupt function is disabled and PENIRQN is forced to "H" state if CSN="H". The behavior of PENIRQN is the same as "ADC ON Mode" Table 3 Power-down Control 0 1 Enabled 1 0 Enabled 1 1 Disabled Serial Interface The AK4180 is controlled via 4-wire serial interface, CSN, DCLK, DIN, DOUT. Please see " Switching Characteristics" for the detail. CSN 1 DCLK DIN BUSY Hi-Z S A2 A1 A0 MO SER/ DFR PD1 PD0 S A2 A1 A0 MO SER/ DFR PD1 PD0 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 DOUT Driver SW SER/ DFR ="1" Hi-Z 11 10 9 8 7 6 5 4 3 2 1 0 11 10 Driver SW SER/ DFR ="0" Figure 5 Serial Interface 12 2003/02 [ASAHI KASEI] [AK4180] BUSY and DOUT goes to "L" from Hi-Z state at the falling edge of CSN. The AK4180 latches the 8bit control word serially via DIN at the rising edge of DCLK. As the AK4180 starts the command decoding at the first "H" bit after CSN="", MSB of the command must be "H". Tracking time is the period from the falling edge of 5th DCLK to the falling edge of 8th DCLK. If SER/ DFR ="1", PD0="0", and if analog input is X-axis or Y-axis (the measurement is the pen position or pen pressure), the touch screen driver switches are turned ON for this 3DCLK period. If SER/ DFR ="0", the switches are turned ON for the period from 5DCLK to 20 DCLK. BUSY is "H" for one DCLK period, which is from 8DCLK to 9DCLK. BUSY is "L" for other period. The AK4180 outputs A/D data with MSB first via DOUT from the falling edge of 9th DCLK. The AK4180 can output one A/D data per 16 DCLK clock cycles for the fastest way as shown in the dotted line of the above figure. Pen Interrupt The AK4180 has pen interrupt function to detect the pen touch. Pen interrupt function is enabled at power-down state. YN pin is connected to GND at the PEN interrupt enabled state. And XP pin is pulled up via an internal resistor (Ri), typically 20k ohm. PENIRQN pulled up via an external resistor, 100k ohm, is also connected to XP pin. If the two plates are touched, the current flows via 13 2003/02 [ASAHI KASEI] [AK4180] 100k PENIRQN EN2 20k EN1 Driver OFF XP YN Driver ON Figure 6 PENIRQ Functional Block Diagram CSN 1 DCLK DIN BUSY 11 10 9 8 7 6 5 4 3 2 1 0 S A2 A1 A0 MO SER/ DFR PD1 PD0 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 DOUT CONV Internal AXIS = ((!A2) & (!A1) & (A0)) | ((!A2) & (A1) & (A0)) | ((A2) & (!A1) & (!A0)) | ((A2) & (!A1) & (A0)); /* X-axis Measurement */ /* Z1 Measurement */ /* Z2 Measurement */ /* Y-axis Measurement */ EN1 = ((!CSN) & (!CONV) & AXIS & PD0) /* CSN="L", X/Y/Z1/Z2 Measurement, PD0 = 1, NOT "CONV period" */ | ((!CSN) & AXIS & CONV); /* CSN="L", X/Y/Z1/Z2 Measurement, "CONV period" */ EN2 = ((!CSN) & (!CONV) & (!PD0)) /* CSN="L", PD0 = 1, NOT "CONV period" */ | (CSN & (!(PD1& PD0)); /* CSN="H", (PD0, PD1) is not (1,1) */ 14 2003/02 [ASAHI KASEI] [AK4180] Package 16pin TSSOP (Unit: mm) 5.00TYP 1.10 MAX 16 9 A 4.4TYP 6.40.2 1 8 0.220.08 | 0.13|M 0.65 1.10 MAX 0.170.05 0.070.04 Detail A 0.50.2 Seating Plane | 0.10 0-10 15 2003/02 [ASAHI KASEI] [AK4180] Marking AKM 4180VT XXYYY Contents of XXYYY XX: Lot # YYY: Date Code 16 2003/02 [ASAHI KASEI] [AK4180] IMPORTANT NOTICE * These products and their specifications are subject to change without notice. Before considering any use or application, consult the Asahi Kasei Microsystems Co., Ltd. (AKM) sales office or authorized distributor concerning their current status. * AKM assumes no liability for infringement of any patent, intellectual property, or other right in the application or use of any information contained herein. * Any export of these products, or devices or systems containing them, may require an export license or other official approval under the law and regulations of the country of export pertaining to customs and tariffs, currency exchange, or strategic materials. * AKM products are neither intended nor authorized for use as critical components in any safety, life support, or other hazard related device or system, and AKM assumes no responsibility relating to any such use, except with the express written consent of the Representative Director of AKM. As used here: (a) A hazard related device or system is one designed or intended for life support or maintenance of safety or for applications in medicine, aerospace, nuclear energy, or other fields, in which its failure to function or perform may reasonably be expected to result in loss of life or in significant injury or damage to person or property. (b)A critical component is one whose failure to function or perform may reasonably be expected to result, whether directly or indirectly, in the loss of the safety or effectiveness of the device or system containing it, and which must therefore meet very high standards of performance and reliability. * It is the responsibility of the buyer or distributor of an AKM product who distributes, disposes of, or otherwise places the product with a third party to notify that party in advance of the above content and conditions, and the buyer or distributor agrees to assume any and all responsibility and liability for and hold AKM harmless from any and all claims arising from the use of said product in the absence of such notification. 17 2003/02 |
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