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general description the max6695/max6696 are precise, dual-remote, and local digital temperature sensors. they accurately mea- sure the temperature of their own die and two remote diode-connected transistors, and report the tempera- ture in digital form on a 2-wire serial interface. the remote diode is typically the emitter-base junction of a common-collector pnp on a cpu, fpga, gpu, or asic. the 2-wire serial interface accepts standard system management bus (smbus) commands such as write byte, read byte, send byte, and receive byte to read the temperature data and program the alarm thresholds and conversion rate. the max6695/max6696 can func- tion autonomously with a programmable conversion rate, which allows control of supply current and temper- ature update rate to match system needs. for conver- sion rates of 2hz or less, the temperature is represented as 10 bits + sign with a resolution of +0.125c. when the conversion rate is 4hz, output data is 7 bits + sign with a resolution of +1c. the max6695/ max6696 also include an smbus timeout feature to enhance system reliability. remote temperature sensing accuracy is 1.5c be- tween +60c and +100c with no calibration needed. the max6695/max6696 measure temperatures from -40c to +125c. in addition to the smbus alert out- put, the max6695/max6696 feature two overtempera- ture limit indicators ( ot1 and ot2 ), which are active only while the temperature is above the corresponding programmable temperature limits. the ot1 and ot2 outputs are typically used for fan control, clock throt- tling, or system shutdown. the max6695 has a fixed smbus address. the max6696 has nine different pin-selectable smbus addresses. the max6695 is available in a 10-pin max ? and the max6696 is available in a 16-pin qsop package. both operate throughout the -40c to +125c temperature range. applications notebook computers desktop computers servers workstations test and measurement equipment features ? measure one local and two remote temperatures ? 11-bit, +0.125c resolution ? high accuracy 1.5c (max) from +60c to +100c (remote) ? acpi compliant ? programmable under/overtemperature alarms ? programmable conversion rate ? three alarm outputs: alert , ot1 , and ot2 ? smbus/i 2 c-compatible interface ? compatible with 65nm process technology (y versions) max6695/max6696 dual remote/local temperature sensors with smbus serial interface ________________________________________________________________ maxim integrated products 1 ordering information typical operating circuit 19-3183; rev 3; 4/11 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. part temp range pin-package max6695 aub+ -40 c to +125 c 10 max MAX6695YAUB+ -40 c to +125 c 10 max max6696 aee+ -40 c to +125 c 16 qsop max6696yaee+ -40 c to +125 c 16 qsop devices are also available in tape-and-reel packages. specify tape and reel by adding t to the part number when ordering. + denotes a lead(pb)-free/rohs-compliant package. pin configurations appear at end of data sheet. clock data to system shutdown gnd ot2 smbclk ot1 smbdata v cc interrupt to p 0.1 f dxn dxp1 47 10k each alert +3.3v cpu to clock throttling dxp2 graphics processor max6695 typical operating circuits continued at end of data sheet. max is a registered trademark of maxim integrated products, inc.
max6695/max6696 dual remote/local temperature sensors with smbus serial interface 2 _______________________________________________________________________________________ absolute maximum ratings stresses beyond those listed under absolute 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. v cc ...........................................................................-0.3v to +6v dxp1, dxp2................................................-0.3v to (v cc + 0.3v) dxn ......................................................................-0.3v to +0.8v smbclk, smbdata, alert ...................................-0.3v to +6v reset, stby , add0, add1, ot1 , ot2 ...................-0.3v to +6v smbdata current .................................................1ma to 50ma dxn current ......................................................................1ma continuous power dissipation (t a = +70c) 10-pin max (derate 6.9mw/c above +70c) ........555.6mw 16-pin qsop (derate 8.3mw/c above +70c) .......666.7mw operating temperature range .........................-40c to +125c junction temperature .....................................................+150c storage temperature range ............................-65c to +150c lead temperature (soldering, 10s) ................................+300c soldering temperature (reflow) .......................................+260c electrical characteristics (v cc = +3.0v to +3.6v, t a = 0c to +125c, unless otherwise noted. typical values are at v cc = +3.3v and t a = +25c) parameter symbol conditions min typ max units supply voltage v cc 3.0 3.6 v standby supply current smbus static, adc in idle state 10 a operating current interface inactive, adc active 0.5 1 ma conversion rate = 0.125hz 35 70 conversion rate = 1hz 250 500 average operating current conversion rate = 4hz 500 1000 a t rj = +25c to +100c (t a = +45c to +85c) -1.5 +1.5 t rj = 0c to +125c (t a = +25c to +100c) -3.0 +3.0 t rj = -40c to +125c (t a = 0c to +125c) -5.0 +5.0 remote temperature error (note 1) t rj = -40c to +125c (t a = -40c) +3.0 c t a = +45c to +85c -2.0 +2.0 t a = +25c to +100c -3.0 +3.0 t a = 0c to +125c -4.5 +4.5 local temperature error t a = -40c to +125c +3.0 c t a = +45c to +85c -3.8 t a = +25c to +100c -4.0 t a = 0c to +125c -4.2 local temperature error (max6695y/max6696y) t a = -40c to +125c -4.4 c power-on reset threshold v cc , falling edge (note 2) 1.3 1.45 1.6 v por threshold hysteresis 500 mv undervoltage lockout threshold uvlo falling edge of v cc disables adc 2.2 2.8 2.95 v undervoltage lockout hysteresis 90 mv channel 1 rate 4hz, channel 2 / local rate 2hz (conversion rate register 05h) 112.5 125 137.5 conversion time channel 1 rate 8hz, channel 2 / local rate 4hz (conversion rate register 06h) 56.25 62.5 68.75 ms high level 80 100 120 remote-diode source current i rj low level 8 10 12 a
max6695/max6696 dual remote/local temperature sensors with smbus serial interface _______________________________________________________________________________________ 3 electrical characteristics (continued) (v cc = +3.0v to +3.6v, t a = 0c to +125c, unless otherwise noted. typical values are at v cc = +3.3v and t a = +25c) parameter symbol conditions min typ max units alert , ot1 , ot2 output low sink current v ol = 0.4v 6 ma output high leakage current v oh = 3.6v 1 a input pin, add0, add1 (max6696) logic input low voltage v il 0.3 v logic input high voltage v ih 2.9 v input pin, reset, stby (max6696) logic input low voltage v il 0.8 v logic input high voltage v ih 2.1 v input leakage current i leak -1 +1 a smbus interface (smbclk, smbdata, stby ) logic input low voltage v il 0.8 v logic input high voltage v ih 2.1 v input leakage current i leak v in = gnd or v cc 1 a output low sink current i ol v ol = 0.6v 6 ma input capacitance c in 5 pf smbus-compatible timing (figures 4 and 5) (note 2) serial clock frequency f scl 10 100 khz bus free time between stop and start condition t buf 4.7 s repeat start condition setup time t su:sta 90% of smbclk to 90% of smbdata 4.7 s start condition hold time t hd:sta 10% of smbdata to 90% of smbclk 4 s stop condition setup time t su:sto 90% of smbclk to 90% of smbdata 4 s clock low period t low 10% to 10% 4 s clock high period t high 90% to 90% 4.7 s data setup time t su:dat 250 ns data hold time t hd:dat 300 ns smb rise time t r 1 s smb fall time t f 300 ns smbus timeout smbdata low period for interface reset 20 30 40 ms note 1: based on diode ideality factor of 1.008. note 2: specifications are guaranteed by design, not production tested.
max6695/max6696 dual remote/local temperature sensors with smbus serial interface 4 _______________________________________________________________________________________ typical operating characteristics (v cc = 3.3v, t a = +25c, unless otherwise noted.) standby supply current vs. supply voltage max6695 toc01 supply voltage (v) standby supply current ( a) 3.5 3.4 3.3 3.2 3.1 1 2 3 4 5 6 0 3.0 3.6 average operating supply current vs. conversion rate control register value max6695 toc02 conversion rate control register value (hex) operating supply current ( a) 3 2 1 100 200 300 400 500 600 0 07 6 5 4 temperature error vs. remote-diode temperature max6695 toc03 remote temperature ( c) temperature error ( c) 100 75 25 50 0 -25 -4 -3 -2 -1 0 1 2 3 4 5 -5 -50 125 remote channel2 remote channel1 local temperature error vs. die temperature max6695 toc04 die temperature ( c) temperature error ( c) 100 75 25 50 0 -25 -4 -3 -2 -1 0 1 2 3 4 5 -5 -50 125 temperature error vs. dxp-dxn capacitance max6695 toc05 dxp-dxn capacitance (nf) temperature error ( c) 3 -3 -2 -1 0 1 2 1 10 100 remote channel1 remote channel2 3 0.001 0.01 0.1 1 10 100 2 1 0 -1 -2 -3 temperature error vs. differential noise frequency max6695 toc06 frequency (mhz) temperature error ( c) remote channel1 v in = 10mv p-p remote channel2 3 0.001 0.01 0.1 1 10 100 2 1 0 -2 -1 -3 remote temperature error vs. power-supply noise frequency max6695 toc07a frequency (mhz) temperature error ( c) 100mv p-p remote channel2 remote channel1 3 0.001 0.01 0.1 1 10 100 2 1 -1 0 -2 -3 local temperature error vs. power-supply noise frequency max6695 toc07b frequency (mhz) temperature error ( c) 100mv p-p 3 0.001 0.01 0.1 1 10 100 2 1 0 -1 -2 -3 temperature error vs. common-mode noise frequency max6695 toc08 frequency (hz) temperature error ( c) remote channel1 10mv p-p remote channel2
max6695/max6696 dual remote/local temperature sensors with smbus serial interface _______________________________________________________________________________________ 5 pin description pin max6695 max6696 name function 1 2 v cc supply voltage input, +3v to +3.6v. bypass to gnd with a 0.1f capacitor. a 47 series resistor is recommended but not required for additional noise filtering. see typical operating circuit . 2 3 dxp1 combined remote-diode current source and a/d positive input for remote-diode channel 1. do not leave dxp1 unconnected; connect dxp1 to dxn if no remote diode is used. place a 2200pf capacitor between dxp1 and dxn for noise filtering. 3 4 dxn combined remote-diode current sink and a/d negative input. dxn is internally biased to one diode drop above ground. 4 5 dxp2 combined remote-diode current source and a/d positive input for remote-diode channel 2. do not leave dxp2 unconnected; connect dxp2 to dxn if no remote diode is used. place a 2200pf capacitor between dxp2 and dxn for noise filtering. 5 10 ot1 overtemperature active-low output, open drain. ot1 is asserted low only when the temperature is above the programmed ot1 threshold. 6 8 gnd ground 7 9 smbclk smbus serial-clock input 8 11 alert smbus alert (interrupt) active-low output, open-drain. asserts when temperature exceeds user-set limits (high or low temperature) or when a remote sensor opens. stays asserted until acknowledged by either reading the status register or by successfully responding to an alert response address. see the alert interrupts section. 9 12 smbdata smbus serial-data input/output, open drain 10 13 ot2 overtemperature active-low output, open drain. ot2 is asserted low only when temperature is above the programmed ot2 threshold. 1, 16 n.c. no connect 6 add1 smbus slave address select input (table 10). add0 and add1 are sampled upon power-up. 7 reset reset input. drive reset high to set all registers to their default values (por state). pull reset low for normal operation. 14 add0 smbus slave address select input (table 10). add0 and add1 are sampled upon power-up. 15 stby hardware standby input. pull stby low to put the device into standby mode. all registers data are maintained.
max6695/max6696 detailed description the max6695/max6696 are temperature sensors designed to work in conjunction with a microprocessor or other intelligence in temperature monitoring, protec- tion, or control applications. communication with the max6695/max6696 occurs through the smbus serial interface and dedicated alert pins. the overtempera- ture alarms ot1 and ot2 are asserted if the software- programmed temperature thresholds are exceeded. ot1 and ot2 can be connected to a fan, system shut- down, or other thermal-management circuitry. the max6695/max6696 convert temperatures to digital data continuously at a programmed rate or by selecting a single conversion. at the highest conversion rate, temperature conversion results are stored in the main temperature data registers (at addresses 00h and 01h) as 7-bit + sign data with the lsb equal to +1 c. at slower conversion rates, 3 additional bits are available at addresses 11h and 10h, providing +0.125 c resolu- tion. see tables 2, 3, and 4 for data formats. adc and multiplexer the max6695/max6696 averaging adc (figure 1) inte- grates over a 62.5ms or 125ms period (each channel, typ), depending on the conversion rate (see electrical characteristics table). the use of an averaging adc attains excellent noise rejection. the max6695/max6696 multiplexer (figure 1) automat- ically steers bias currents through the remote and local diodes. the adc and associated circuitry measure each diodes forward voltages and compute the tem- perature based on these voltages. if a remote channel is not used, connect dxp_ to dxn. do not leave dxp_ and dxn unconnected. when a conversion is initiated, all channels are converted whether they are used or not. the dxn input is biased at one v be above ground by an internal diode to set up the adc inputs for a dif- ferential measurement. resistance in series with the remote diode causes about +1/2c error per ohm. a/d conversion sequence a conversion sequence consists of a local temperature measurement and two remote temperature measure- ments. each time a conversion begins, whether initiat- ed automatically in the free-running autoconvert mode (run/stop = 0) or by writing a one-shot command, all three channels are converted, and the results of the three measurements are available after the end of con- version. because it is common to require temperature measurements to be made at a faster rate on one of the remote channels than on the other two channels, the conversion sequence is remote 1, local, remote 1, remote 2. therefore, the remote 1 conversion rate is double that of the conversion rate for either of the other two channels. a busy status bit in status register 1 (see table 7 and the status byte functions section) shows that the device is actually performing a new conversion. the results of the previous conversion sequence are always available when the adc is busy. remote-diode selection the max6695/max6696 can directly measure the die temperature of cpus and other ics that have on-board temperature-sensing diodes (see the typical operating 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 max6695/max6696 (not the max6695y/max6696y) are optimized for n = 1.008. a thermal diode on the substrate of an ic is normally a pnp with its collector grounded. dxp_ must be connected to the anode (emitter) and dxn must be connected to the cathode (base) of this pnp. if a sense transistor with an ideality factor other than 1.008 is used, the output data will be different from the data obtained with the optimum ideality factor. fortunately, the difference is predictable. assume a remote-diode sensor designed for a nominal ideality factor n nominal is used to measure the temperature 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 and n nomimal for the max6695/max6696 is 1.008. as an example, assume you want to use the max6695 or max6696 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 +85c (358.15k), the measured temperature is +82.87c (356.02k), an error of -2.13c. effect of series resistance series resistance (r s ) with a sensing diode contributes additional error. for nominal diode currents of 10a tt n n t actual m nominal m = ? ? ? ? ? ? = ? ? 1 1 008 1 002 . . ? ? ? ? ? = () t m 1 00599 . tt n n m actual nominal = ? ? ? ? ? ? 1 dual remote/local temperature sensors with smbus serial interface 6 _______________________________________________________________________________________
and 100a, the change in the measured voltage due to series resistance is: since 1c corresponds to 198.6v, series resistance contributes a temperature offset of: assume that the sensing diode being measured has a series resistance of 3 . the series resistance con- tributes a temperature offset of: 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: 1.36c - 2.13c = -0.77c for a diode temperature of +85c. 3 0 453 1 36 =+ .. c c 90 198 6 0 453 v v c c . . = vaarar mss =?= () 100 10 90 ? max6695/max6696 dual remote/local temperature sensors with smbus serial interface _______________________________________________________________________________________ 7 ot2 ot1 alert dxp2 dxn dxp1 reset/ uvlo circuitry v cc (reset) mux remote1 remote2 local q s r ot2 thresholds alert response address alert threshold local temperatures remote temperatures command byte register bank q s r q s r adc control logic 8 8 smbus read write (stby) smbdata smbclk (add0) (add1) address decoder 3 diode fault () are for max6696 only. 7 ot1 thresholds figure 1. max6695/max6696 functional diagram
max6695/max6696 in this example, the effect of the series resistance and the ideality factor partially cancel each other. discrete remote diodes when the remote-sensing diode is a discrete transistor, its collector and base must be connected together. table 1 lists examples of discrete transistors that are appropriate for use with the max6695/max6696. 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 10a, and at the lowest expected tempera- ture, the forward voltage must be less than 0.95v at 100a. 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 v be characteristics. manufacturers of discrete transistors do not normally specify or guarantee ideality factor. this is normally not a problem since good-quality discrete transistors tend to have ideality factors that fall within a relatively narrow range. we have observed variations in remote tempera- ture readings of less than 2 c with a variety of dis- crete transistors. still, it is good design practice to verify good consistency of temperature readings with several discrete transistors from any manufacturer under consideration. thermal mass and self-heating when sensing local temperature, these temperature sensors are intended to measure the temperature of the pc board to which they are soldered. the leads pro- vide a good thermal path between the pc board traces and the die. as with all ic temperature sensors, thermal conductivity between the die and the ambient air is poor by comparison, making air temperature measure- ments impractical. because the thermal mass of the pc board is far greater than that of the max6695/ max6696, the device follows temperature changes on the pc board with little or no perceivable delay. when measuring the temperature of a cpu or other ic with an on-chip sense junction, thermal mass has virtu- ally no effect; the measured temperature of the junction tracks the actual temperature within a conversion cycle. when measuring temperature with discrete remote transistors, the best thermal response times are obtained with transistors in small packages (i.e., sot23 or sc70). take care to account for thermal gradients between the heat source and the sensor, and ensure that 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. for local temperature mea- surements, the worst-case error occurs when autocon- verting at the fastest rate and simultaneously sinking maximum current at the alert output. for example, with v cc = 3.6v, a 4hz conversion rate and alert sinking 1ma, the typical power dissipation is: j-a for the 16-pin qsop package is about +120c/w, so assuming no copper pc board heat sinking, the resulting temperature rise is: even under these worst-case circumstances, it is diffi- cult to introduce significant self-heating errors. adc noise filtering the integrating adc has good noise rejection for low- frequency signals such as power-supply hum. in envi- ronments with significant high-frequency emi, connect an external 2200pf capacitor between dxp_ and dxn. larger capacitor values can be used for added filter- ing, but do not exceed 3300pf because it can intro- duce errors due to the rise time of the switched current source. high-frequency noise reduction is needed for high-accuracy remote measurements. noise can be reduced with careful pc board layout as discussed in the pc board layout section. low-power standby mode standby mode reduces the supply current to less than 10a by disabling the adc. enter hardware standby (max6696 only) by forcing stby low, or enter software standby by setting the run /stop bit to 1 in the config- tmw cw c ==+ 2 2 120 0 264 ./. vavmamw cc += 500 0 4 1 2 2 .. dual remote/local temperature sensors with smbus serial interface 8 _______________________________________________________________________________________ manufacturer model no. central semiconductor (usa) cmpt3904 rohm semiconductor (usa) sst3904 samsung (korea) kst3904-tf siemens (germany) smbt3904 zetex (england) fmmt3904ct-nd table 1. remote-sensor transistor manufacturers note: discrete transistors must be diode connected (base shorted to collector).
uration byte register. hardware and software standbys are very similar; all data is retained in memory, and the smbus interface is alive and listening for smbus com- mands but the smbus timeout is disabled. the only dif- ference is that in software standby mode, the one-shot command initiates a conversion. with hardware stand- by, the one-shot command is ignored. activity on the smbus causes the device to draw extra supply current. driving stby low overrides any software conversion command. if a hardware or software standby command is received while a conversion is in progress, the con- version cycle is interrupted, and the temperature regis- ters are not updated. the previous data is not changed and remains available. smbus digital interface from a software perspective, the max6695/max6696 appear as a series of 8-bit registers that contain tem- perature data, alarm threshold values, and control bits. a standard smbus-compatible 2-wire serial interface is used to read temperature data and write control bits and alarm threshold data. the same smbus slave address provides access to all functions. the max6695/max6696 employ four standard smbus protocols: write byte, read byte, send byte, and receive byte (figure 2). the shorter receive byte proto- col allows quicker transfers, provided that the correct data register was previously selected by a read byte instruction. use caution with the shorter protocols in mul- timaster systems, since a second master could overwrite the command byte without informing the first master. when the conversion rate control register is set 06h, temperature data can be read from the read internal temperature (00h) and read external temperature (01h) registers. the temperature data format in these regis- ters is 7 bits + sign in twos-complement form for each channel, with the lsb representing +1c (table 2). the msb is transmitted first. use bit 3 of the configuration register to select the registers corresponding to remote 1 or remote 2. when the conversion rate control register is set 05h, temperature data can be read from the read internal temperature (00h) and read external temperature (01h) registers, the same as for faster conversion rates. an additional 3 bits can be read from the read external extended temperature register (10h) and read internal max6695/max6696 dual remote/local temperature sensors with smbus serial interface _______________________________________________________________________________________ 9 figure 2. smbus protocols ack 7 bits address ack wr 8 bits data ack 1 p 8 bits s command 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) ack 7 bits address ack wr s ack 8 bits data 7 bits address rd 8 bits /// p command slave address: equiva- lent 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 ack 7 bits address wr 8 bits command ack p ack 7 bits address rd 8 bits data /// p s 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
max6695/max6696 extended temperature register (11h) (table 3), which extends the temperature data to 10 bits + sign and the resolution to +0.125c per lsb (table 4). when a conversion is complete, the main register and the extended register are updated almost simultane- ously. ensure that no conversions are completed between reading the main and extended registers so that when data that is read, both registers contain the result of the same conversion. to ensure valid extended data, read extended resolu- tion temperature data using one of the following approaches: ? put the max6695/max6696 into standby mode by setting bit 6 of the configuration register to 1. read the contents of the data registers. return to run mode by setting bit 6 to zero. ? put the max6695/max6696 into standby mode by setting bit 6 of the configuration register to 1. initiate a one-shot conversion using send byte command 0fh. when this conversion is complete, read the contents of the temperature data registers. diode fault alarm there is a continuity fault detector at dxp_ that detects an open circuit between dxp_ and dxn, or a dxp_ short to v cc , gnd, or dxn. if an open or short circuit exists, the external temperature register (01h) is loaded with 1000 0000. bit 2 (diode fault) of the status registers is correspondingly set to 1. the alert output asserts for open diode faults but not for shorted diode faults. immediately after power-on reset (por), the status reg- ister indicates that no fault is present until the end of the first conversion. after the conversion is complete, any diode fault is indicated in the appropriate status register. reading the status register clears the diode fault bit in that register, and clears the alert output if set. if the diode fault is present after the next conver- sion, the status bit will again be set and the alert out- put will assert if the fault is an open diode fault. alarm threshold registers six registers, wlho, wllm, wrha (1 and 2), and wrln (1 and 2), store alert threshold values. wlho and wllm, are for internal alert high-temperature and low-temperature limits, respectively. likewise, wrha and wrln are for external channel 1 and chan- nel 2 high-temperature and low-temperature limits, respectively (table 5). if either measured temperature equals or exceeds the corresponding alert threshold value, the alert output is asserted. the por state of both internal and external alert high-temperature limit registers is 0100 0110 or +70c. dual remote/local temperature sensors with smbus serial interface 10 ______________________________________________________________________________________ temp ( c) digital output +130.00 0 111 1111 +127.00 0 111 1111 +126.00 0 111 1110 +25.25 0 001 1001 +0.50 0 000 0001 0 0 000 0000 -1 1 111 1111 -55 1 100 1001 diode fault (short or open) 1 000 0000 table 2. data format (twos complement) fractional temperature ( c) contents of extended register 0 000x xxxx +0.125 001x xxxx +0.250 010x xxxx +0.375 011x xxxx +0.500 100x xxxx +0.625 101x xxxx +0.750 110x xxxx +0.875 111x xxxx table 3. extended resolution register note: extended resolution applies only for conversion rate control register values of 05h or less. temp ( c) integer temp fractional temp +130.00 0 111 1111 000x xxxx +127.00 0 111 1111 000x xxxx +126.5 0 111 1110 100x xxxx +25.25 0 001 1001 010x xxxx +0.50 0 000 0000 100x xxxx 0 0 000 0000 000x xxxx -1 1 111 1111 000x xxxx -1.25 1111 1111 010x xxxx -55 1100 1001 000x xxxx table 4. data format in extended mode
max6695/max6696 dual remote/local temperature sensors with smbus serial interface ______________________________________________________________________________________ 11 register address por state function rlts 00 h 0000 0000 (0 c) read internal temperature rrte 01 h 0000 0000 (0 c) read external channel 1 temperature if bit 3 of configuration register is 0 ; read external channel 2 temperature if bit 3 of configuration register is 1 rsl1 02 h 1000 0000 read status register 1 rcl 03 h 0000 0000 read configuration byte (fault queue should be disabled at startup) rcra 04 h 0000 0110 read conversion rate byte rlhn 05 h 0100 0110 (+70 c) read internal alert high limit rlli 06 h 1100 1001 (-55 c) read internal alert low limit rrhi 07 h 0100 0110 (+70 c) read external channel 1 alert high limit if bit 3 of configuration register is 0 ; read external channel 2 alert high limit if bit 3 of configuration register is 1 rrls 08 h 1100 1001 (-55 c) read external channel 1 alert low limit if bit 3 of configuration register is 0 ; read external channel 2 alert low limit if bit 3 of configuration register is 1 wca 09 h 0010 0000 write configuration byte wcrw 0a h 0000 0110 write conversion rate byte wlho 0b h 0100 0110 (+70 c) write internal alert high limit wllm 0c h 1100 1001 (-55 c) write internal alert low limit wrha 0d h 0100 0110 (+70 c) write external channel 1 alert high limit if bit 3 of configuration register is 0 ; write external channel 2 alert high limit if bit 3 of configuration register is 1 wrln 0e h 1100 1001 (-55 c) write external channel 1 alert low limit if bit 3 of configuration register is 0 ; write external channel 2 alert low limit if bit 3 of configuration register is 1 osht 0f h 0000 0000 one shot reet 10 h 0000 0000 read extended temp of external channel 1 if bit 3 of configuration register is 0 ; read extended temp of external channel 2 if bit 3 of configuration register is 1 riet 11 h 0000 0000 read internal extended temperature rsl2 12 h 0000 0000 read status register 2 rwo2e 16 h 0111 1000 (+120 c) read/write external ot2 limit for channel 1 if bit 3 of configuration register is 0 ; read/write external ot2 limit for channel 2 if bit 3 of configuration register is 1 rwo2i 17 h 0101 1010 (+90 c) read/write internal ot2 limit rwo1e 19 h 0101 1010 (+90 c) read/write external ot1 limit for channel 1 if bit 3 of configuration register is 0 ; read/write external ot1 limit for channel 2 if bit 3 of configuration register is 1 rwo1i 20 h 0100 0110 (+70 c) read/write internal ot1 limit table 5. command-byte register bit assignments
max6695/max6696 the por state of both internal and external alert low- temperature limit registers is 1100 1001 or -55c. use bit 3 of the configuration register to select remote 1 or remote 2 when reading or writing remote thresholds. additional registers, rwo1e, rwo1i, rwo2e, and rwo2i, store remote and local alarm threshold data information corresponding to the ot1 and ot2 outputs (see the ot1 and ot2 overtemperature alarms section.) alert interrupt mode an alert interrupt occurs when the internal or external temperature reading exceeds a high- or low-tempera- ture limit (both limits are user programmable), or when the remote diode is disconnected (for continuity fault detection). the alert interrupt output signal is latched and can be cleared only by reading either of the status registers or by successfully responding to an alert response address. in both cases, the alert is cleared but is reasserted at the end of the next conversion if the fault condition still exists. the interrupt does not halt automatic conversions. the interrupt output pin is open drain so that multiple devices can share a common interrupt line. the interrupt rate never exceeds the con- version rate. alert response address the smbus alert response interrupt pointer provides quick fault identification for simple slave devices. upon receiving an interrupt signal, the host master can broadcast a receive byte transmission to the alert response slave address (see slave addresses sec- tion). then, any slave device that generated an inter- rupt attempts to identify itself by putting its own address on the bus. the alert response can activate several different slave devices simultaneously, similar to the i 2 c general call. if more than one slave attempts to respond, bus arbitra- tion rules apply, and the device with the lower address code wins. the losing device does not generate an acknowledgement and continues to hold the alert line low until cleared. (the conditions for clearing an alert vary depending on the type of slave device.) successful completion of the alert response protocol clears the interrupt latch, provided the condition that caused the alert no longer exists. if the condition still exists, the device reasserts the alert interrupt at the end of the next conversion. ot1 and ot2 overtemperature alarms two registers, rwo1e and rwo1i, store remote and local alarm threshold data corresponding to the ot1 output. two other registers, rwo2e and rwo2i, store remote and local alarm threshold data corresponding to the ot2 output. the values stored in these registers are high-temperature thresholds. the ot1 or ot2 out- put is asserted if any one of the measured tempera- tures equals or exceeds the corresponding alarm threshold value. ot1 and ot2 always operate in comparator mode and are asserted when the temperature rises above a value programmed in the appropriate threshold register. they are deasserted when the temperature drops below this threshold, minus the programmed value in the hystere- sis hyst register (21h). an overtemperature output can be used to activate a cooling fan, send a warning, initi- ate clock throttling, or trigger a system shutdown to prevent component damage. the hyst byte sets the amount of hysteresis to deassert both ot1 and ot2 outputs. the data format for the hyst byte is 7 bit + sign with +1c resolution. bit 7 of the hyst register should always be zero. ot1 responds immediately to temperature faults. ot2 activates either immediately or after four consecu- tive remote channel temperature faults, depending on the state of the fault queue bit (bit 5 of the configura- tion register). command byte functions the 8-bit command byte register (table 5) is the master index that points to the various other registers within the max6695/max6696. this registers por state is 0000 0000, so a receive byte transmission (a protocol that lacks the command byte) occurring immediately after por returns the current local temperature data. one-shot the one-shot command immediately forces a new con- version cycle to begin. if the one-shot command is received when the max6695/max6696 are in software standby mode ( run /stop bit = 1), a new conversion is dual remote/local temperature sensors with smbus serial interface 12 ______________________________________________________________________________________ register address por state function hyst 21 h 0000 1010 (10 c) temperature hysteresis for ot1 and ot2 rdid fe h 4d h read manufacturer id table 5. command-byte register bit assignments (continued)
begun, after which the device returns to standby mode. if a conversion is in progress when a one-shot com- mand is received, the command is ignored. if a one- shot command is received in autoconvert mode ( run /stop bit = 0) between conversions, a new con- version begins, the conversion rate timer is reset, and the next automatic conversion takes place after a full delay elapses. fault queue function to avoid false triggering of the max6695/max6696 in noisy environments, a fault queue is provided, which can be enabled by setting bit 5 (configuration register) to 1. four channel 1 fault or two channel 2 fault events must occur consecutively before the fault output (ot2) becomes active. any reading that breaks the sequence resets the fault queue counter. if there are three over- limit readings followed by a within-limit reading, the remote channel 1 fault queue counter is reset. configuration byte functions the configuration byte register (table 6) is a read-write register with several functions. bit 7 is used to mask (disable) alert interrupts. bit 6 puts the device into software standby mode (stop) or autonomous (run) mode. bit 5, when 1, enables the fault queue. bit 4 is reserved. bit 3 is used to select either remote channel 1 or remote channel 2 for reading temperature data or for setting or reading temperature limits. bit 2 disables the smbus timeout, as well as the alert response. bit 1 masks alert interrupt due to channel 2 when high. bit 0 masks alert interrupt due to channel 1 when high. status byte functions the status registers (tables 7 and 8) indicate which (if any) temperature thresholds have been exceeded and if there is an open-circuit fault detected with the exter- nal sense junctions. status register 1 also indicates whether the adc is converting. after por, the normal state of the registers bits is zero (except bit 7 of status register 1), assuming no alert or overtemperature con- ditions are present. bits 0 through 6 of status register 1 and bits 1 through 7 of status register 2 are cleared by any successful read of the status registers, unless the fault persists. the alert output follows the status flag bit. both are cleared when successfully read, but if the condition still exists, they reassert at the end of the next conversion. the bits indicating ot1 and ot2 are cleared only on reading status even if the fault conditions still exist. reading the status byte does not clear the ot1 and ot2 outputs. one way to eliminate the fault condition is for the measured temperature to drop below the tem- perature threshold minus the hysteresis value. another way to eliminate the fault condition is by writing new values for the rwo2e, rwo2i, rwo1e, rwo1i, or hyst registers so that a fault condition is no longer present. when autoconverting, if the t high and t low limits are close together, it is possible for both high-temp and low-temp status bits to be set, depending on the amount of time between status read operations. in these circumstances, it is best not to rely on the status bits to indicate reversals in long-term temperature changes. instead, use a current temperature reading to establish the trend direction. max6695/max6696 dual remote/local temperature sensors with smbus serial interface ______________________________________________________________________________________ 13 bit name por state function 7(msb) mask1 0 mask alert interrupts when 1. 6 run /stop 0 standby mode control bit. if 1, immediately stops converting and enters standby mode. if zero, it converts in either one-shot or timer mode. 5 fault queue 0 fault queue enables when 1. when set to 1, four consecutive faults must occur before ot2 output is asserted. 4 rfu 0 reserved. 3 remote 2 select 0 0: read/write remote 1 temperature and set-point values. 1: read/write remote 2 temperature and set-point values. 2 smb timeout disable 0 when set to 1, it disables the smbus timeout, as well as the alert response. 1 mask alert channel 2 0 when set to 1, it masks alert interrupt due to channel 2. 0 mask alert channel 1 0 when set to 1, it masks alert interrupt due to channel 1. table 6. configuration byte functions
max6695/max6696 reset (max6696 only) the max6696s registers are reset to their power-on values if reset is driven high. when reset occurs, all registers go to their default values, and the smbus address pins are sampled. conversion rate byte the conversion-rate control register (table 9) programs the time interval between conversions in free-running autonomous mode ( run /stop = 0). this variable rate control can be used to reduce the supply current in portable-equipment applications. the conversion rate dual remote/local temperature sensors with smbus serial interface 14 ______________________________________________________________________________________ bit name por function 7(msb) busy 1 a/d is busy converting when 1. 6 lhigh 0 when 1, internal high-temperature alert has tripped, cleared by por or by reading this status register. if the fault condition still exists, this bit is set again after the next conversion. 5 llow 0 when 1, internal low-temperature alert has tripped, cleared by por or by reading this status register. if the fault condition still exists, this bit is set again after the next conversion. 4 r1high 0 a 1 indicates external junction 1 high-temperature alert has tripped, cleared by por or by reading this status register. if the fault condition still exists, this bit is set again after the next conversion. 3 r1low 0 a 1 i nd i cates exter nal j uncti on 1 l ow - tem p er atur e ale rt has tr i p p ed , cl ear ed b y p or or b y r ead i ng thi s status r eg i ster . if the faul t cond i ti on sti l l exi sts, thi s b i t i s set ag ai n after the next conver si on. 2 1open 0 a 1 indicates external diode 1 is open, cleared by por or by reading this status register. if the fault condition still exists, this bit is set again after the next conversion. 1 r1ot1 0 a 1 indicates external junction 1 temperature exceeds the ot1 threshold, cleared by reading this register. 0 iot1 0 a 1 indicates internal junction temperature exceeds the internal ot1 threshold, cleared by reading this register. table 7. status register 1 bit assignments bit name por function 7(msb) iot2 0 a 1 indicates internal junction temperature exceeds the internal ot2 threshold, cleared by reading this register. 6 r2ot2 0 a 1 indicates external junction temperature 2 exceeds the external ot2 threshold, cleared by reading this register. 5 r1ot2 0 a 1 indicates external junction temperature 1 exceeds the ot2 threshold, cleared by reading this register. 4 r2high 0 a 1 indicates external junction 2 high-temperature alert has tripped; cleared by por or readout of the status register. if the fault condition still exists, this bit is set again after the next conversion. 3 r2low 0 a 1 indicates external junction 2 low-temperature alert has tripped; cleared by por or readout of the status register. if the fault condition still exists, this bit is set again after the next conversion. 2 2open 0 a 1 indicates external diode 2 open; cleared by por or readout of the status register. if the fault condition still exists, this bit is set again after the next conversion. 1 r2ot1 0 a 1 indicates external junction 2 temperature exceeds the ot1 threshold, cleared by reading this register. 0 rfu 0 reserved. table 8. status register 2 bit assignments
bytes por state is 06h (4hz). the max6695/max6696 use only the 3 lsbs of the control register. the 5 msbs are dont care and should be set to zero. the conver- sion rate tolerance is 25% at any rate setting. valid a/d conversion results for all channels are avail- able one total conversion time after initiating a conver- sion, whether conversion is initiated through the run /stop bit, hardware stby pin, one-shot com- mand, or initial power-up. slave addresses the max6695 has a fixed address of 0011 000. the max6696 device address can be set to any one of nine different values at power-up by pin strapping add0 and add1 so that more than one max6695/max6696 can reside on the same bus without address conflicts (table 10). the address pin states are checked at por and reset only, and the address data stays latched to reduce qui- escent supply current due to the bias current needed for high-impedance state detection. the max6695/ max6696 also respond to the smbus alert response slave address (see the alert response address section). por and uvlo to prevent unreliable power-supply conditions from corrupting the data in memory and causing erratic behavior, a por voltage detector monitors v cc and clears the memory if v cc falls below 1.45v (typ; see electrical characteristics ). when power is first applied and v cc rises above 2.0v (typ), the logic blocks begin operating, although reads and writes at v cc levels below 3.0v are not recommended. power-up defaults ? interrupt latch is cleared. ? address select pin is sampled. ? adc begins autoconverting at a 4hz rate for channel 2/local and 8hz for channel 1. ? command register is set to 00h to facilitate quick internal receive byte queries. ?t high and t low registers are set to default max and min limits, respectively. ? hysteresis is set to 10 c. max6695/max6696 dual remote/local temperature sensors with smbus serial interface ______________________________________________________________________________________ 15 bit 3 bit 1 bit0 hex conversion rate (hz) remote channel 2 and local conversion rate (hz) remote channel 1 conversion period (s) remote channel 2 and local conversion period (s) remote channel 1 0 0 0 00h 0.0625 0.125 16 8 0 0 1 01h 0.125 0.25 8 4 0 1 0 02h 0.25 0.5 4 2 0 1 1 03h 0.5 1 2 1 1 0 0 04h 1 2 1 0.5 1 0 1 05h 2 4 0.5 0.25 1 1 0 06h 4 8 0.25 0.125 1 1 1 07h 4 8 0.25 0.125 table 9. conversion-rate control register (por = 0110) add0 add1 address gnd gnd 0011 000 gnd high-z 0011 001 gnd v cc 0011 010 high-z gnd 0101 001 high-z high-z 0101 010 high-z v cc 0101 011 v cc gnd 1001 100 v cc high-z 1001 101 v cc v cc 1001 110 table 10. por slave address decoding (add0 and add1) note: extended resolution applies only for conversion rate control register values of 05h or less.
max6695/max6696 pc board layout follow these guidelines to reduce the measurement error when measuring remote temperature: 1) place the max6695/max6696 as close as is practi- cal to the remote diode. in noisy environments, such as a computer motherboard, this distance can be 4in to 8in (typ). this length can be increased if the worst noise sources are avoided. noise sources include crts, clock generators, memory buses, and 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 +30c error, even with good filtering. 3) route the dxp and dxn traces in parallel and in close proximity to each other. each parallel pair of traces (dxp1 and dxn or dxp2 and dxn) should go to a remote diode. connect the two dxn traces at the max6695/max6696. route these traces away from any higher voltage traces, such as +12vdc. dual remote/local temperature sensors with smbus serial interface 16 ______________________________________________________________________________________ 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 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 3. smbus write timing diagram 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 l m 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 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 4. smbus read timing diagram
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 5). 4) route through as few vias and crossunders as pos- sible to minimize copper/solder thermocouple effects. 5) use wide traces when practical. 6) when the power supply is noisy, add a resistor (up to 47 ) in series with v cc (see typical operating circuit ). twisted-pair and shielded cables use a twisted-pair cable to connect the remote sensor for remote-sensor distances 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 shielded twisted pair like that used for audio micro- phones. for example, belden #8451 works well for dis- tances 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 cables parasitic capaci- tance often provides noise filtering, so the 2200pf capacitor can often be removed or reduced in value. cable resistance also affects remote-sensor accuracy. for every 1 of series resistance the error is approxi- mately +1/2c. chip information process: bicmos max6695/max6696 dual remote/local temperature sensors with smbus serial interface ______________________________________________________________________________________ 17 minimum 10 mils 10 mils 10 mils 10 mils gnd dxn dxp gnd figure 5. recommended dxp-dxn pc traces typical operating circuits (continued) clock data to system shutdown stby reset gnd add1 ot2 smbclk ot1 smbdata v cc interrupt to p 0.1 f dxn dxp1 47 10k each alert +3.3v add0 max6696 cpu 2n3906 dxp2 to clock throttling
max6695/max6696 dual remote/local temperature sensors with smbus serial interface 18 ______________________________________________________________________________________ 1 2 3 4 5 10 9 8 7 6 ot2 smbdata alert smbclk dxp2 dxn dxp1 v cc max6695 max top view gnd ot1 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 n.c. n.c. stby add0 ot2 smbdata ot1 smbclk max6696 qsop v cc dxp1 add1 dxn dxp2 reset gnd alert pin configurations package information for the latest package outline information and land patterns (footprints), go to www.maxim-ic.com/packages . note that a +, #, or - in the package code indicates rohs status only. package drawings may show a different suffix character, but the drawing per tains to the package regardless of rohs status. package type package code outline no. land pattern no. 10 max u10cn+1 21-0061 90-0330 16 qsop e16+1 21-0055 90-0167
max6695/max6696 dual remote/local temperature sensors with smbus serial interface 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 ____________________ 19 ? 2011 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. revision history revision number revision date description pages changed 0 2/04 initial release 1 5/04 removed future status from max6696 in the ordering information table; updated the ot1 and ot2 overtemperature alarms section 1, 12 2 11/05 updated the features section, ordering information table, electrical characteristics table, and effect of ideality factor section 1, 2, 6 3 4/11 added lead(pb)-free and tape-and-reel options to the ordering information table; added soldering information to the absolute maximum ratings section; corrected the units for data setup time and data hold time from s to ns in the electrical characteristics table; added the package information table 1, 2, 3, 18

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