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general description the MAX6641 temperature sensor and fan controller accurately measures the temperature of its own die and the temperature of a remote pn junction. the device reports temperature values in digital form using a 2-wire serial interface. the remote pn junction is typically the emitter-base junction of a common-collector pnp on a cpu, fpga, or asic. the 2-wire serial interface accepts standard system management bus (smbus) tm write byte, read byte, send byte, and receive byte commands to read the temperature data and program the alarm thresholds. the temperature data controls a pwm output signal to adjust the speed of a cooling fan, thereby minimizing noise when the system is running cool, but providing maximum cooling when power dissipation increases. the device also features an over-temperature alarm output to generate interrupts, throttle signals, or shut down signals. the MAX6641 operates from supply volt- ages in the 3.0v to 5.5v range and typically consumes 500? of supply current. the MAX6641 is available in a slim 10-pin ?ax pack- age and is available over the automotive temperature range (-40 c to +125 c). applications desktop computers notebook computers workstations servers networking equipment industrial features ? tiny 3mm x 5mm ?ax package ? thermal diode input ? local temperature sensor ? open-drain pwm output for fan drive ? programmable fan control characteristics ? automatic fan spin-up ensures fan start ? ?? remote temperature accuracy (+60? to +145?) ? controlled rate of change ensures unobtrusive fan-speed adjustments ? temperature monitoring begins at power-on for fail-safe system protection ? ot output for throttling or shutdown MAX6641 smbus-compatible temperature monitor with automatic pwm fan-speed controller ________________________________________________________________ maxim integrated products 1 ordering information 19-3304; rev 0; 5/04 for pricing, delivery, and ordering information, please contact maxim/dallas direct! at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. part temp range pin- package smbus address MAX6641aub90 -40 c to +125 c 10 ?ax 1001 000x MAX6641aub92 -40 c to +125 c 10 ?ax 1001 001x MAX6641aub94 -40 c to +125 c 10 ?ax 1001 010x MAX6641aub96 -40 c to +125 c 10 ?ax 1001 011x 1 2 3 4 5 10 9 8 7 6 pwmout v cc smbdata smbclk gnd dxp dxn i.c. MAX6641 max top view i.c. ot pin configuration ?ax is a registered trademark of maxim integrated products, inc. smbus is a trademark of intel corp. typical application circuit appears at end of data sheet.
MAX6641 smbus-compatible temperature monitor with automatic pwm fan-speed controller 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v cc = +3.0v to +5.5v, t a = 0 c to +125 c, unless otherwise noted. typical values are at v cc = 3.3v, t a = +25 c.) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. all voltages referenced to gnd v cc , ot , smbdata, smbclk, pwmout...............-0.3v to +6v dxp .........................................................?0.3v to (v cc + 0.3v) dxn ......................................................................-0.3v to +0.8v esd protection (all pins, human body model) .......?000v continuous power dissipation (t a = +70?) 10-pin ?ax (derate 5.6mw/? above +70?) .......... 444mw operating temperature range .........................-40? to +125? junction temperature ......................................................+150? storage temperature range ............................-65? to +150? lead temperature (soldering, 10s) ............................... +300? parameter symbol conditions min typ max units operating supply voltage range v cc 3.0 5.5 v operating current smbdata, smbclk not switching 0.5 1 ma +25? t r +125?, t a = +60? ? 0c t r +145c, +25? t a = +100? ? external temperature error v cc = 3.3v 0c t r +145c, 0c t a +125c ? ? +25c t a +100c -2.5 +2.5 internal temperature error v cc = 3.3v 0c t a +125c -4 +4 ? 1c temperature resolution 8 bits conversion time 200 250 300 ms pwm frequency tolerance -20 +20 % high level 80 100 120 remote-diode sourcing current low level 8 10 12 ? dxn source voltage 0.7 v i/o ot , smbdata, pwmout output low voltage v ol i out = 6ma 0.4 v ot , smbdata, pwmout output-high leakage current i oh v cc = 5.5v 1 a smbdata, smbclk logic-low input voltage v il v cc = 3v to 5.5v 0.8 v smbdata, smbclk logic-high input voltage v ih v cc = 3v to 5.5v 2.1 v smbdata, smbclk leakage current 1a smbdata, smbclk input capacitance c in 5pf
MAX6641 smbus-compatible temperature monitor with automatic pwm fan-speed controller _______________________________________________________________________________________ 3 note 1: timing specifications guaranteed by design. note 2: the serial interface resets when smbclk is low for more than t timeout . note 3: a transition must internally provide at least a hold time to bridge the undefined region (300ns max) of smbclk? falling edge. electrical characteristics (continued) (v cc = +3.0v to +5.5v, t a = 0 c to +125 c, unless otherwise noted. typical values are at v cc = 3.3v, t a = +25 c.) parameter symbol conditions min typ max units smbus-compatible timing (note 1) (see figures 2, 3) serial clock frequency f sclk (note 2) 100 khz clock low period t low 10% to 10% 4 s clock high period t high 90% to 90% 4.7 ? bus free time between stop and start condition t buf 4.7 ? hold time after (repeated) start condition t hd:sta 4s s m bus s tar t c ond i ti on s etup ti m e t su:sta 90% of smbclk to 90% of smbdata 4.7 ? start condition hold time t hd:sto 10% of smbdata to 10% of smbclk 4 s stop condition setup time t su:sto 90% of smbclk to 10% of smbdata 4 s data setup time t su:dat 10% of smbdata to 10% of smbclk 250 ns data hold time t hd:dat 10% of smbclk to 10% of smbdata (note 3) 300 ns smbus fall time t f 300 ns smbus rise time t r 1000 ns smbus timeout t timeout 29 37 55 ms startup time after por t por 500 ms t ypical operating characteristics (v cc = 3.3v, t a = +25 c, unless otherwise noted.) operating supply current vs. supply voltage MAX6641 toc01 supply voltage (v) operating supply current ( a) 5.0 4.5 4.0 3.5 350 400 450 500 550 600 300 3.0 5.5 no smbus activity remote temperature error vs. remote-diode temperature MAX6641 toc02 temperature ( c) temperature error ( c) 100 75 25 50 -1.5 -1.0 -0.5 0 0.5 1.0 1.5 2.0 -2.0 0125 local temperature error vs. die temperature MAX6641 toc03 temperature ( c) temperature error ( c) 100 75 50 25 -1 0 1 2 -2 0125
MAX6641 smbus-compatible temperature monitor with automatic pwm fan-speed controller 4 _______________________________________________________________________________________ remote temperature error vs. power-supply noise frequency MAX6641 toc04 frequency (khz) temperature error ( c) 100 10 1 -1.25 -1.00 -0.75 -0.50 -0.25 0 -1.50 0.1 1000 t a = +80 c, 250mv square wave applied at v cc , no bypass capacitor local temperature error vs. power-supply noise frequency MAX6641 toc05 frequency (khz) temperature error ( c) 100 10 1 -1.5 -1.0 -0.5 0 0.5 1.0 -2.0 0.1 1000 t a = +25 c, 250mv square wave applied at v cc , no bypass capacitor remote temperature error vs. common-mode noise frequency MAX6641 toc06 frequency (khz) temperature error ( c) 100 10 1 -1.0 -0.5 0 0.5 1.0 -1.5 0.1 1000 t a = +80 c, v in = 100mv p-p square wave applied to dxp remote temperature error vs. differential-mode noise frequency MAX6641 toc07 frequency (khz) temperature error ( c) 100 10 1 -0.5 0 0.5 1.0 1.5 -1.0 0.1 1000 t a = +80 c, v in = 10mv p-p square wave applied to dxp - dxn remote temperature error vs. dxp - dxn capacitance MAX6641 toc08 dxp - dxn capacitance (nf) normalized temperature error ( c) 10 1 -4 -3 -2 -1 0 1 2 3 -5 0.1 100 t a = +80 c pwm frequency error vs. die temperature MAX6641 toc09 temperature ( c) pwm frequency error (hz) 100 75 50 25 0 -25 -2 -1 0 1 2 -3 -50 125 pwm frequency error vs. supply voltage MAX6641 toc10 supply voltage (v) pwm frequency error (hz) 5.0 4.5 4.0 3.5 -0.5 0 0.5 1.0 1.5 2.0 -1.0 3.0 5.5 t a = +25 c t ypical operating characteristics (continued) (v cc = 3.3v, t a = +25 c, unless otherwise noted.)
detailed description the MAX6641 temperature sensor and fan controller accurately measures the temperature of its own die and the temperature of a remote pn junction. the device reports temperature values in digital form using a 2- wire serial interface. the remote pn junction is typically the emitter-base junction of a common-collector pnp on a cpu, fpga, or asic. the MAX6641 operates from supply voltages of 3.0v to 5.5v and consumes 500? of supply current. the temperature data controls a pwm output signal to adjust the speed of a cooling fan. the device also features an over-temperature alarm output to generate interrupts, throttle signals, or shut down signals. smbus digital interface from a software perspective, the MAX6641 appears as a set of byte-wide registers that contain temperature data, alarm threshold values, and control bits. a stan- dard smbus-compatible 2-wire serial interface is used to read temperature data and write control bits and alarm threshold data. these devices respond to the same smbus slave address for access to all functions. the MAX6641 employs four standard smbus protocols: write byte, read byte, send byte, and receive byte (figures 1, 2, and 3). the shorter receive byte protocol allows quicker transfers, provided that the correct data register was previously selected by a read byte instruc- tion. use caution when using the shorter protocols in multimaster systems, as a second master could over- write the command byte without informing the first mas- ter. the MAX6641 has four different slave addresses available; therefore, a maximum of four MAX6641 devices can share the same bus. temperature data within the 0? to +255? range can be read from the read external temperature register (00h). temperature data within the 0c to +125? range can be read from the read internal temperature register (01h). the temperature data format for these registers is 8 bits, with the lsb representing +1? ( table 1) and the msb representing +128?. the msb is transmitted first. all values below 0? are clipped to 00h. table 1 details the register address and function, whether they can be read or written to, and the power-on reset (por) state. see tables 1? for all other register functions and the register descriptions section. figure 4 is the MAX6641 block diagram. MAX6641 smbus-compatible temperature monitor with automatic pwm fan-speed controller _______________________________________________________________________________________ 5 pin name function 1, 6 i.c. internally connected. must be connected to gnd. 2dxn combined remote-diode cathode connection and a/d negative input. connect the cathode of the remote-diode-connected transistor to dxn. 3 dxp combined remote-diode current source and a/d positive input for remote-diode channel. connect dxp to the anode of a remote-diode-connected temperature-sensing transistor. do not leave dxp floating ; connect to dxn if no remote diode is used. place a 2200pf capacitor between dxp and dxn for noise filtering. 4 gnd ground 5 ot active-low, open-drain, over-temperature output. use ot as an interrupt, a system shutdown signal, or to control clock throttling. ot can be pulled up to 5.5v, regardless of the voltage on v cc . ot is high impedance when v cc = 0. 7 smbclk smbus serial clock input. smbclk can be pulled up to 5.5v, regardless of v cc . open drain. smbclk is high impedance when v cc = 0. 8 smbdata smbus serial data input/output. smbdata can be pulled up to 5.5v, regardless of v cc . open drain. smbdata is high impedance when v cc = 0. 9v cc positive supply. bypass with a 0.1? capacitor to gnd. 10 pwmout pwm output to fan power transistor. connect pwmout to the gate of a mosfet or the base of a bipolar transistor to drive the fan? power supply with a pwm waveform. alternatively, the pwm output can be connected to the pwm input of a fan with direct speed-control capability, or it can be converted to a dc voltage for driving the fan? power supply. pwmout requires a pullup resistor. the pullup resistor can be connected to a voltage supply up to 5.5v, regardless of v cc . pin description
MAX6641 smbus-compatible temperature monitor with automatic pwm fan-speed controller 6 _______________________________________________________________________________________ read/ write register address por state function/ name d7 d6 d5 d4 d3 d2 d1 d0 r 00h 0000 0000 read remote (external) temperature msb (+128 c) (+64 c) (+32 c) (+16 c) (+8 c) (+4 c) (+2 c) lsb (+1 c) r 01h 0000 0000 read local (internal) temperature msb (+128 c) (+64 c) (+32 c) (+16 c) (+8 c) (+4 c) (+2 c) lsb (+1 c) r/w 02h 0000 00xx configuration byte reserved set to 0 reserved set to 0 timeout: 0 = enabled, 1 = disabled fan pwm invert min duty cycle: 0 = 0%, 1 = fan- start duty cycle spin-up disable xx r/w 03h 0110 1110 remote-diode temperature ot limit msb (+128 c) (+64 c) (+32 c) (+16 c) (+8 c) (+4 c) (+2 c) lsb (+1 c) r/w 04h 0101 0000 local-diode temperature ot limit msb (+128 c) (+64 c) (+32 c) (+16 c) (+8 c) (+4 c) (+2 c) lsb (+1 c) r 05h 00xx xxxx ot status remote 1 = fault local 1 = fault xxxxxx r/w 06h 00xx xxxx ot mask remote 1 = masked local 1 = masked xxxxxx r/w 07h 0110 000x (96 = 40%) fan-start duty cycle msb (128/240) (64/240) (32/240) ( 16/240) (8/240) (4/240) lsb (2/240) x r/w 08h 1111 000x (240 = 100%) fan maximum duty cycle msb (128/240) (64/240) (32/240) ( 16/240) (8/240) (4/240) lsb (2/240) x r/w 09h 0000 000x fan target duty cycle msb (128/240) (64/240) (32/240) ( 16/240) (8/240) (4/240) lsb (2/240) x r 0ah 0000 000x fan instantaneous duty cycle msb (128/240) (64/240) (32/240) ( 16/240) (8/240) (4/240) lsb (2/240) x r/w 0bh 0000 0000 remote-diode fan-start temperature msb (+128 c) (+64 c) (+32 c) (+16 c) (+8 c) (+4 c) (+2 c) lsb (+1 c) table 1. register functions
MAX6641 smbus-compatible temperature monitor with automatic pwm fan-speed controller _______________________________________________________________________________________ 7 read/ write register address por state function/ name d7 d6 d5 d4 d3 d2 d1 d0 r/w 0ch 0000 0000 local-diode fan-start temperature msb (+128 c) (+64 c) (+32 c) (+16 c) (+8 c) (+4 c) (+2 c) lsb (+1 c) r/w 0dh 0000 xxxx fan configuration h yster esi s: 0 = 5 c , 1 = 10 c temp step: 0 = 1 c, 1 = 2 c fan control: 1 = remote fan control: 1 = local xxxx r/w 0eh 101x xxxx duty-cycle rate of change msb lsb xxxxx r/w 0fh 0101 xxxx duty-cycle step size msb lsb xxxx r/w 10h 010x xxxx pwm frequency select select a select b select c xxxxx r fdh 0000 0001 read device revision 00 0 00001 r feh 1000 0111 read device id 10 0 00111 r ffh 0100 1101 read manufacturer id 01 0 01101 table 1. register functions (continued) x = don? care. see register descriptions for further details.
MAX6641 smbus-compatible temperature monitor with automatic pwm fan-speed controller 8 _______________________________________________________________________________________ write byte format read byte format send byte format receive byte format slave address: equiva- lent to chip-select line of a 3-wire interface command byte: selects which register you are writing to data byte: data goes into the register set by the command byte (to set thresholds, configuration masks, and sampling rate) slave address: equivalent to chip-select line command byte: selects which register you are reading from slave address: repeated due to change in data- flow direction data byte: reads from the register set by the command byte command byte: sends com- mand with no data, usually used for one-shot command data byte: reads data from the register commanded by the last read byte or write byte transmission; also used for smbus alert response return address s = start condition shaded = slave transmission p = stop condition /// = not acknowledged figure 1. smbus protocols s address rd ack data /// p 7 bits 8 bits wr s ack command ack p 8 bits address 7 bits p 1 ack data 8 bits ack command 8 bits ack wr address 7 bits s s address wr ack command ack s address 7 bits 8 bits 7 bits rd ack data 8 bits /// p smbclk a = start condition b = msb of address clocked into slave c = lsb of address clocked into slave d = r/w bit clocked into slave ab cd e fg hij smbdata t su:sta t hd:sta t low t high t su:dat t su:sto t buf lm k e = slave pulls smbdata line low f = acknowledge bit clocked into master g = msb of data clocked into slave h = lsb of data clocked into slave i = master pulls data line low j = acknowledge clocked into slave k = acknowledge clock pulse l = stop condition m = new start condition figure 2. smbus write timing diagram
register descriptions temperature registers (00h, 01h) these registers contain the 8-bit results of the tempera- ture measurements. register 00h contains the tempera- ture reading of the remote diode. register 01h contains the ambient temperature reading. the value of the msb is +128 c and the value of the lsb is +1 c. the msb is transmitted first. the por state of the temperature reg- isters is 00h. configuration byte register (02h) the configuration byte register controls the timeout conditions and various pwmout signals. the por state of the configuration byte register is 00h. see table 2 for configuration byte definitions. remote and local ot limits (03h, 04h) set the remote (03h) and local (04h) temperature thresh- olds with these two registers. once the temperature is above the threshold, the ot output is asserted low (for the temperature channels that are not masked). the por state of the remote ot limit register is 6eh and the por state of the local ot limit register is 50h. ot status (05h) read the ot status register to determine which channel recorded an over-temperature condition. bit d7 is high if the fault reading occurred from the remote diode. bit d6 is high if the fault reading occurred in the local diode. the ot status register is cleared only by reading its con- tents. reading the contents of the register also makes the ot output high impedance. if the fault is still present on the next temperature measurement cycle, the corre- sponding bits and the ot output are set again. after reading the ot status register, a temperature register read must be done to correctly clear the appropriate sta- tus bit. the por state of the ot status register is 00h. MAX6641 smbus-compatible temperature monitor with automatic pwm fan-speed controller _______________________________________________________________________________________ 9 smbclk ab cd e fg h i j k smbdata t su:sta t hd:sta t low t high t su:dat t hd:dat t su:sto t buf a = start condition b = msb of address clocked into slave c = lsb of address clocked into slave d = r/w bit clocked into slave e = slave pulls smbdata line low l m f = acknowledge bit clocked into master g = msb of data clocked into master h = lsb of data clocked into master i = master pulls data line low j = acknowledge clocked into slave k = acknowledge clock pulse l = stop condition m = new start condition figure 3. smbus read timing diagram figure 4. block diagram gnd smbus interface and registers logic pwm generator block v cc temperature processing block smbdata smbclk dxp dxn pwmout ot MAX6641
MAX6641 smbus-compatible temperature monitor with automatic pwm fan-speed controller 10 ______________________________________________________________________________________ bit name por state function 7 0 reserved. set to zero. 6 0 reserved. set to zero. 5 timeout 0 set timeout to zero to enable smbus timeout for prevention of bus lockup. set to 1 to disable this function. 4 fan pwm invert 0 set fan pwm invert to zero to force pwmout low when the duty cycle is 100%. set to 1 to force pwmout high when the duty cycle is 100%. 3 min duty cycle 0 set min duty cycle to zero for a 0% duty cycle when the measured temperature is below the fan-temperature threshold in automatic mode. when the temperature equals the fan-temperature threshold, the duty cycle is the value in the fan-start duty-cycle register, which increases with increasing temperature. set min duty cycle to 1 to force the pwm duty cycle to the value in the fan-start duty-cycle register when the measured temperature is below the fan-temperature threshold. as the temperature increases above the temperature threshold, the duty cycle increases as programmed. 2 spin-up disable 0 set spin-up disable to 1 to disable spin-up. set to zero for normal fan spin-up. 1 x don? care. 0 x don? care. table 2. configuration byte definition (02h) ot mask (06h) set bit d7 to 1 in the ot mask register to prevent the ot output from asserting on faults in the remote-diode temperature channel. set bit d6 to 1 to prevent the ot output from asserting on faults in the local-diode tem- perature channel. the por state of the ot mask regis- ter is 00h. fan-start duty cycle (07h) the fan-start duty-cycle register determines the pwm duty cycle where the fan starts spinning. bit d3 in the configuration byte register (min duty cycle) deter- mines the starting duty cycle. if the min duty cycle bit is 1, the duty cycle is the value written to the fan- start duty-cycle register at all temperatures below the fan-start temperature. if the min duty cycle bit is zero, the duty cycle is zero below the fan-start tempera- ture and has this value when the fan-start temperature is reached. a value of 240 represents 100% duty cycle. writing any value greater than 240 causes the fan speed to be set to 100%. the por state of the fan-start duty-cycle register is 60h, 40%. fan maximum duty cycle (08h) the fan maximum duty-cycle register sets the maxi- mum allowable pwmout duty cycle between 2/240 (0.83% duty cycle) and 240/240 (100% duty cycle). any values greater than 240 are recognized as 100% maximum duty cycle. the por state of the fan maxi- mum duty-cycle register is f0h, 100%. in manual con- trol mode, this register is ignored. fan-target duty cycle (09h) in automatic fan-control mode, this register contains the present value of the target pwm duty cycle, as deter- mined by the measured temperature and the duty- cycle step size. the actual duty cycle needs a settling time before it equals the target duty cycle if the duty- cycle rate of change register is set to a value other than zero. the actual duty cycle needs the time to settle as defined by the value of the duty-cycle rate-of-change register; therefore, the target duty cycle and the actual duty cycle are often different. in manual fan-control mode, write the desired value of the pwm duty cycle directly into this register. the por state of the fan-tar- get duty-cycle register is 00h.
MAX6641 smbus-compatible temperature monitor with automatic pwm fan-speed controller ______________________________________________________________________________________ 11 fan instantaneous duty cycle (0ah) read the fan instantaneous duty-cycle register to deter- mine the duty cycle at pwmout at any time. the por state of the fan instantaneous duty-cycle register is 00h. remote- and local-diode fan-start temperature (0bh, 0ch) these registers contain the temperature threshold val- ues at which fan control begins in automatic mode. see the automatic pwm duty-cycle control section for details on setting the fan-start thresholds. the por state of the remote- and local-diode fan-start tempera- ture registers is 00h. fan configuration (0dh) the fan-configuration register controls the hysteresis level, temperature step size, and whether the remote or local diode controls the pwmout signal; see table 1. set bit d7 of the fan-configuration register to zero to set the hysteresis value to 5 c. set bit d7 to 1 to set the hysteresis value to 10 c. set bit d6 to zero to set the fan-control temperature step size to 1 c. set bit d6 to 1 to set the fan-control temperature step size to 2 c. set bit d5 to 1 to control the fan with the remote-diode? temperature reading. set bit d4 to 1 to control the fan with the local-diode? temperature reading. if both bits d5 and d4 are high, the device uses the highest pwm value. if both bits d5 and d4 are zero, the MAX6641 runs in manual fan-control mode where only the value written to the fan-target duty-cycle register (09h) con- trols the pwmout duty cycle. in manual fan-control mode, the value written to the fan-target duty-cycle reg- ister is not limited by the value in the maximum duty- cycle register. it is, however, clipped to 240 if a value above 240 is written. the por state of the fan-configu- ration register is 00h. duty-cycle rate of change (0eh) bits d7, d6, and d5 of the duty-cycle rate-of-change register set the time between increments of the duty cycle. each increment is 2/240 of the duty cycle; see table 3. this allows the time from 33% to 100% duty cycle to be adjusted from 5s to 320s. the rate-of- change control is always active in manual mode. to make instant changes, set bits d7, d6, d5 = 000. the por state of the duty-cycle rate-of-change register is a0h (1s time between increments). duty-cycle step size (0fh) bits d7?4 of the duty-cycle step-size register change the size of the duty-cycle change for each temperature step. the por state of the duty-cycle step-size register is 50h; see table 4. pwm frequency select (10h) set bits d7, d6, and d5 (select a, select b, and select c) in the pwm frequency-select register to control the pwmout frequency; see table 5. the por state of the pwm frequency select register is 40h, 33hz. the lower frequencies are usually used when driving the fan? power-supply pin as in the typical application circuit , with 33hz being the most common choice. the 35khz d7, d6, d5 time between increments (s) time from 33% to 100% (s) 000 0 0 001 0.0625 5 010 0.1250 10 011 0.2500 20 100 0.5000 40 101 1.0000 80 110 2.0000 160 111 4.0000 320 table 3. duty-cycle rate-of-change register (0eh) d7?4 change in duty cycle per temperature step temperature range for fan control (1 c step, 33% to 100%) 0000 0/240 n/a 0001 2/240 80.00 0010 4/240 40.00 0011 6/240 26.67 0100 8/240 20.00 0101 10/240 16.00 0110 12/240 13.33 0111 14/240 11.43 1000 16/240 10.00 1001 18/240 8.89 1010 20/240 8.00 1011 22/240 7.27 1100 24/240 6.67 1101 26/240 6.15 1110 28/240 5.71 1111 30/240 5.33 table 4. duty-cycle step-size register (0fh)
frequency setting is used for controlling fans that have logic-level pwm input pins for speed control. duty- cycle resolution is decreased from 2/240 to 4/240 at the 35khz frequency setting. pwm output the pwmout signal is normally used in one of three ways to control the fan? speed: 1) pwmout drives the gate of a mosfet or the base of a bipolar transistor in series with the fan? power supply. the typical application circuit shows the pwmout pin driving an n-channel mosfet. in this case, the pwm invert bit (d4 in register 02h) is set to 1. figure 5 shows pwmout driving a p-channel mosfet and the pwm invert bit must be set to zero. 2) pwmout is converted (using an external circuit) into a dc voltage that is proportional to duty cycle. this duty-cycle-controlled voltage becomes the power supply for the fan. this approach is less effi- cient than 1), but can result in quieter fan operation. figure 6 shows an example of a circuit that con- verts the pwm signal to a dc voltage. because this circuit produces a full-scale output voltage when pwmout = 0v, bit d4 in register 02h should be set to zero. 3) pwmout directly drives the logic-level pwm speed-control input on a fan that has this type of input. this approach requires fewer external com- ponents and combines the efficiency of 1) with the low noise of 2). an example of pwmout driving a fan with a speed-control input is shown in figure 7. bit d4 in register 02h should be set to 1 when this configuration is used. whenever the fan has to start turning from a motionless state, pwmout is forced high for 2s. after this spin-up period, the pwmout duty cycle settles to the predeter- mined value. if spin-up is disabled (bit 2 in the configu- ration byte = 1), the duty cycle changes immediately from zero to the nominal value, ignoring the duty-cycle rate-of-change setting. MAX6641 smbus-compatible temperature monitor with automatic pwm fan-speed controller 12 ______________________________________________________________________________________ pwm frequency (hz) select a select b select c 20 00 0 33 01 0 50 10 0 100 11 0 35k xx 1 table 5. pwm frequency select (10h) v cc pwmout 10k ? 5v p figure 5. driving a p-channel mosfet for top-side pwm fan drive +3.3v pwmout 18k ? 27k ? 10k ? 120k ? p +3.3v +12v 500k ? v out to fan 1 f 1 f 0.01 f figure 6. driving a fan with a pwm-to-dc circuit v cc pwmout 4.7k ? 5v figure 7. controlling a pwm input fan with the MAX6641? pwm output (typically, the 35khz pwm frequency is used)
MAX6641 smbus-compatible temperature monitor with automatic pwm fan-speed controller ______________________________________________________________________________________ 13 the frequency-select register controls the frequency of the pwm signal. when the pwm signal modulates the power supply of the fan, a low pwm frequency (usually 33hz) should be used to ensure the circuitry of the brushless dc motor has enough time to operate. when driving a fan with a pwm-to-dc circuit, as in figure 6, the highest available frequency (35khz) should be used to minimize the size of the filter capacitors. when using a fan with a pwm control input, the frequency should normally be high as well, although some fans have pwm inputs that accept low-frequency drive. the duty cycle of the pwm can be controlled in two ways: 1) manual pwm control by setting the duty cycle of the fan directly through the fan-target duty-cycle register (09h). 2) automatic pwm control by setting the duty cycle based on temperature. manual pwm duty-cycle control setting bits d5 and d4 to zero in the fan-configuration register (0dh) enables manual pwmout control. in this mode, the duty cycle written to the fan-target duty- cycle register controls the pwmout duty cycle. the value is clipped to a maximum of 240, which corre- sponds to a 100% duty cycle. any value above that is limited to the maximum duty cycle. in manual control mode, the value of the maximum duty-cycle register is ignored and does not affect the duty cycle. automatic pwm duty-cycle control in the automatic control mode, the duty cycle is con- trolled by the local or remote temperature, according to the settings in the control registers. below the value of the fan-start temperature threshold (set by registers 03h and 04h), the duty cycle is equal to the fan-start duty cycle. above the fan-start temperature, the duty cycle increases by one duty-cycle step each time the tempera- ture increases by one temperature step. below the fan- start temperature, the duty cycle is either 0% or it is equal to the fan-start duty cycle, depending on the value of bit d3 in the configuration byte register. see figure 8. the target duty cycle is calculated based on the follow- ing formula: for temperature > fan-start temperature: where: dc = dutycycle fsdc = fanstartdutycycle t = temperature fst = fanstarttemperature dcss = dutycyclestepsize ts = tempstep duty cycle is recalculated after each temperature con- version if temperature is increasing. if the temperature begins to decrease, the duty cycle is not recalculated until the temperature drops by 5 c from the last peak temperature. the duty cycle remains the same until the temperature drops 5 c from the last peak temperature or the temperature rises above the last peak tempera- ture. for example, if temperature goes up to +85 c and starts decreasing, duty cycle is not recalculated until the temperature reaches +80 c or the temperature rises above +85 c. if temperature decreases further, the duty cycle is not updated until it reaches +75 c. for temperature < fan-start temperature and bit d3 of the configuration byte register = 0: dutycycle = 0 for temperature < fan-start temperature and bit d3 of the configuration byte register = 1: dutycycle = fanstartdutycycle once the temperature crosses the fan-start tempera- ture threshold, the temperature has to drop below the fan-start temperature threshold minus the hysteresis before the duty cycle returns to either 0% or fan-start duty cycle. the value of the hysteresis is set by d7 of the fan-configuration register. dc fsdc t fst dcss ts =+ ( ) - f an start duty cycle temperature duty cycle register 02h, bit d3 = 1 duty cycle step size f an start temperature temp step register 02h, bit d3 = 0 figure 8. automatic pwm duty control
MAX6641 smbus-compatible temperature monitor with automatic pwm fan-speed controller 14 ______________________________________________________________________________________ the duty cycle is limited to the value in the fan maxi- mum duty-cycle register. if the duty-cycle value is larg- er than the maximum fan duty cycle, it can be set to the maximum fan duty cycle as in the fan maximum duty- cycle register. the temp step is bit d6 of the fan-config- uration register (0dh). if duty cycle is an odd number, the MAX6641 automati- cally rounds down to the nearest even number. duty-cycle rate-of-change control to reduce the audibility of changes in fan speed, the rate of change of the duty cycle is limited by the values set in the duty-cycle rate-of-change register. whenever the target duty cycle is different from the instantaneous duty cycle, the duty cycle increases or decreases at the rate determined by the duty-cycle rate-of-change byte until it reaches the target duty cycle. by setting the rate of change to the appropriate value, the thermal requirements of the system can be balanced against good acoustic performance. slower rates of change are less noticeable to the user, while faster rates of change can help minimize temperature variations. remember that the fan controller is part of a complex control system. because several of the parameters are generally not known, some experimentation may be necessary to arrive at the best settings. power-up defaults at power-up, the MAX6641 has the default settings indicated in table 1. some of these settings are sum- marized below: temperature conversions are active. remote ot limit = +110 c. local ot limit = +80 c. manual fan mode. fan duty cycle = 0. pwm invert bit = 0. pwmout is high. when using an nmos or npn transistor, the fan starts at full speed on power-up. applications information remote-diode selection the MAX6641 can directly measure the die tempera- ture of cpus and other ics that have on-board temper- ature-sensing diodes (see the typical application circuit ), or they can measure the temperature of a dis- crete diode-connected transistor. effect of ideality factor the accuracy of the remote temperature measurements depends on the ideality factor (n) of the remote diode (actually a transistor). the MAX6641 is optimized for n = 1.008, which is the typical value for the intel pentium?iii and the amd athlon mp model 6. if a sense transistor with a different ideality factor is used, the output data is different. fortunately, the difference is predictable. assume a remote-diode sensor designed for a nominal ideality factor n nominal is used to measure the tem- perature of a diode with a different ideality factor, n 1 . the measured temperature t m can be corrected using: where temperature is measured in kelvin. as mentioned above, the nominal ideality factor of the MAX6641 is 1.008. as an example, assume the MAX6641 is configured with a cpu that has an ideality factor of 1.002. if the diode has no series resistance, the mea- sured data is related to the real temperature as follows: for a real temperature of +85? (358.15k), the mea- sured temperature is +82.87? (356.02k), which is an error of -2.13?. effect of series resistance series resistance in a sense diode contributes addition- al errors. for nominal diode currents of 10? and 100?, change in the measured voltage is: ? v m = r s (100? - 10?) = 90? x r s since 1? corresponds to 198.6?, series resistance contributes a temperature offset of: assume that the diode being measured has a series resistance of 3 ? . the series resistance contributes an offset of: : 30 453 1 36 ? ? =+ .. c c 90 198 6 0 453 ? = ? v v c c . . tt n n tt actual m m m nominal = ? ? ? ? ? ? == () ? ? ? ? ? ? 1 1 008 1 002 1 00599 . . . tt n n m actual nominal = ? ? ? ? ? ? 1 pentium is a registered trademark of intel corp. athlon is a trademark of amd.
MAX6641 smbus-compatible temperature monitor with automatic pwm fan-speed controller ______________________________________________________________________________________ 15 the effects of the ideality factor and series resistance are additive. if the diode has an ideality factor of 1.002 and series resistance of 3 ? , the total offset can be cal- culated by adding error due to series resistance with error due to ideality factor: 1.36? - 2.13? = -0.1477? for a diode temperature of +85?. in this example, the effect of the series resistance and the ideality factor partially cancel each other. for best accuracy, the discrete transistor should be a small-signal device with its collector connected to gnd and base connected to dxn. table 6 lists examples of discrete transistors that are appropriate for use with the MAX6641. the transistor must be a small-signal type with a rela- tively high forward voltage; otherwise, the a/d input voltage range can be violated. the forward voltage at the highest expected temperature must be greater than 0.25v at 10?, and at the lowest expected tempera- ture, the forward voltage must be less than 0.95v at 100?. large power transistors must not be used. also, ensure that the base resistance is less than 100 ? . tight specifications for forward-current gain (50 < ?<150, for example) indicate that the manufacturer has good process controls and that the devices have consistent vbe characteristics. adc noise filtering the integrating adc used has good noise rejection for low-frequency signals such as 60hz/120hz power-sup- ply hum. in noisy environments, high-frequency noise reduction is needed for high-accuracy remote measure- ments. the noise can be reduced with careful pc board layout and proper external noise filtering. high-frequency emi is best filtered at dxp and dxn with an external 2200pf capacitor. larger capacitor values can be used for added filtering, but do not exceed 3300pf because larger values can introduce errors due to the rise time of the switched current source. pc board layout follow these guidelines to reduce the measurement error of the temperature sensors: 1) place the MAX6641 as close as is practical to the remote diode. in noisy environments, such as a computer motherboard, this distance can be 4in to 8in typically. this length can be increased if the worst noise sources are avoided. noise sources include crts, clock generators, memory buses, and isa/pci buses. 2) do not route the dxp-dxn lines next to the deflec- tion coils of a crt. also, do not route the traces across fast digital signals, which can easily intro- duce 30? error, even with good filtering. 3) route the dxp and dxn traces in parallel and in close proximity to each other, away from any higher voltage traces, such as 12vdc. leakage currents from pc board contamination must be dealt with carefully since a 20m ? leakage path from dxp to ground causes about 1c error. if high-voltage traces are unavoidable, connect guard traces to gnd on either side of the dxp-dxn traces (figure 9). 4) route through as few vias and crossunders as pos- sible to minimize copper/solder thermocouple effects. 5) when introducing a thermocouple, make sure that both the dxp and the dxn paths have matching thermocouples. a copper-solder thermocouple exhibits 3?/?, and takes about 200? of voltage error at dxp-dxn to cause a 1? measurement error. adding a few thermocouples causes a negli- gible error. 6) use wide traces. narrow traces are more inductive and tend to pick up radiated noise. the 10-mil widths and spacing recommended in figure 9 are not absolutely necessary, as they offer only a minor improvement in leakage and noise over narrow traces. use wider traces when practical. 7) add a 200 ? resistor in series with v cc for best noise filtering (see the typical application circuit ). 8) copper cannot be used as an emi shield; only fer- rous materials such as steel work well. placing a copper ground plane between the dxp-dxn traces and traces carrying high-frequency noise signals does not help reduce emi. manufacturer model no. central semiconductor (usa) cmpt3906 rohm semiconductor (usa) sst3906 samsung (korea) kst3906-tf siemens (germany) smbt3906 table 6. remote-sensor transistor manufacturers
twisted-pair and shielded cables use a twisted-pair cable to connect the remote sensor for remote-sensor distance longer than 8in or in very noisy environments. twisted-pair cable lengths can be between 6ft and 12ft before noise introduces excessive errors. for longer distances, the best solution is a shield- ed twisted pair like that used for audio microphones. for example, belden 8451 works well for distances up to 100ft in a noisy environment. at the device, connect the twisted pair to dxp and dxn and the shield to gnd. leave the shield unconnected at the remote sensor. for very long cable runs, the cable? parasitic capaci- tance often provides noise filtering, so the 2200pf capac- itor can often be removed or reduced in value. cable resistance also affects remote-sensor accuracy. for every 1 ? of series resistance, the error is approximately 0.5?. thermal mass and self-heating when sensing local temperature, these devices are intended to measure the temperature of the pc board to which they are soldered. the leads provide a good thermal path between the pc board traces and the die. thermal conductivity between the die and the ambient air is poor by comparison, making air temperature mea- surements impractical. because the thermal mass of the pc board is far greater than that of the MAX6641, the devices follow temperature changes on the pc board with little or no perceivable delay. when measur- ing the temperature of a cpu or other ic with an on- chip sense junction, thermal mass has virtually no effect. the measured temperature of the junction tracks the actual temperature within a conversion cycle. when measuring temperature with discrete remote sen- sors, smaller packages, such as ?axes, yield the best thermal response times. take care to account for thermal gradients between the heat source and the sensor, and ensure stray air currents across the sensor package do not interfere with measurement accuracy. self-heating does not significantly affect measurement accuracy. remote-sensor self-heating due to the diode current source is negligible. MAX6641 smbus-compatible temperature monitor with automatic pwm fan-speed controller 16 ______________________________________________________________________________________ minimum 10 mils 10 mils 10 mils 10 mils gnd dxn dxp gnd figure 9. recommended dxp-dxn pc traces MAX6641 gnd v cc (3.0v to 5.5v) smbdata smbclk dxp dxn 5v v fan (5v or 12v) to clock throttle or system shutdown pwmout p 5v 2200pf 10k ? each 10k ? 0.1 f ot t ypical application circuit chip information transistor count: 18,769 process: bicmos
MAX6641 smbus-compatible temperature monitor with automatic pwm fan-speed controller maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ____________________ 17 2004 maxim integrated products printed usa is a registered trademark of maxim integrated products. package information (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation, go to www.maxim-ic.com/packages .) package information (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation, go to www.maxim-ic.com/packages .) 10lumax.eps package outline, 10l umax/usop 1 1 21-0061 i rev. document control no. approval proprietary information title: top view front view 1 0.498 ref 0.0196 ref s 6 side view bottom view 0 0 6 0.037 ref 0.0078 max 0.006 0.043 0.118 0.120 0.199 0.0275 0.118 0.0106 0.120 0.0197 bsc inches 1 10 l1 0.0035 0.007 e c b 0.187 0.0157 0.114 h l e2 dim 0.116 0.114 0.116 0.002 d2 e1 a1 d1 min - a 0.940 ref 0.500 bsc 0.090 0.177 4.75 2.89 0.40 0.200 0.270 5.05 0.70 3.00 millimeters 0.05 2.89 2.95 2.95 - min 3.00 3.05 0.15 3.05 max 1.10 10 0.60.1 0.60.1 00.5 0 0.1 h 4x s e d2 d1 b a2 a e2 e1 l l1 c gage plane a2 0.030 0.037 0.75 0.95 a1

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