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________________general description the max1619 is a precise digital thermometer that reports the temperature of both a remote sensor and its own package. the remote sensor is a diode-connected transis- tor?ypically a low-cost, easily mounted 2n3904 npn type?hat replaces conventional thermistors or thermo- couples. remote accuracy is ?? for multiple transistor manufacturers, with no calibration needed. the remote channel can also measure the die temperature of other ics, such as microprocessors, that contain an on-chip, diode-connected transistor. the 2-wire serial interface accepts standard system management bus (smbus ) write byte, read byte, send byte, and receive byte commands to program the alarm thresholds and to read temperature data. the data format is 7 bits plus sign, with each bit corresponding to 1c, in two? complement format. measurements can be done automatically and autonomously, with the conversion rate programmed by the user or programmed to operate in a single-shot mode. the adjustable rate allows the user to control the supply-current drain. the max1619 is nearly identical to the popular max1617a, with the additional feature of an overtemperature alarm out- put ( overt ) that responds to the remote temperature; this is optimal for fan control. ________________________applications desktop and notebook central office computers telecom equipment smart battery packs test and measurement lan servers multichip modules industrial controls ____________________________features ? two channels measure both remote and local temperatures ? no calibration required ? smbus 2-wire serial interface ? programmable under/overtemperature alarms ? overt output for fan control ? supports smbus alert response ? supports manufacturer and device id codes ? accuracy ?? (+60? to +100?, local) ?? (-40? to +125?, local) ?? (+60? to +100?, remote) ? 3? (typ) standby supply current ? 70? (max) supply current in auto-convert mode ? +3v to +5.5v supply range ? write-once protection ? small 16-pin qsop package max1619 remote/local temperature sensor with dual- alarm outputs and smbus serial interface ________________________________________________________________ maxim integrated products 1 max1619 smbclk add0 add1 v cc stby gnd alert smbdata dxp dxn interrupt to m c fan control +3v to +5.5v 200 w 0.1 m f clock 10k each data 2n3904 2200pf overt ___________________pin configuration 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 v cc n.c. stby smbclk n.c. smbdata alert add0 overt top view max1619 qsop gnd dxp add1 dxn n.c. gnd gnd typical operating circuit 19-1483; rev 0; 4/99 part MAX1619MEE -55? to +125? temp. range pin-package 16 qsop ordering information smbus is a registered trademark of intel corp. for free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. for small orders, phone 1-800-835-8769.
max1619 remote/local temperature sensor with dual- alarm outputs and smbus serial interface 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v cc = +3.3v, t a = 0? to +85? , configuration byte = xch, unless otherwise noted.) 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. v cc to gnd ..............................................................-0.3v to +6v dxp, add_ to gnd ....................................-0.3v to (v cc + 0.3v) dxn to gnd ..........................................................-0.3v to +0.8v smbclk, smbdata, alert , overt , stby to gnd............................................................-0.3v to +6v smbdata, alert, overt current....................-1ma to +50ma dxn current .......................................................................?ma esd protection (all pins, human body model) ..................2000v continuous power dissipation (t a = +70?) qsop (derate 8.30mw/? above +70?) .....................667mw operating temperature range .........................-55? to +125? junction temperature ......................................................+150? storage temperature range .............................-65? to +150? lead temperature (soldering, 10sec) .............................+300? t a = +60? to +100? monotonicity guaranteed add0, add1; momentary upon power-on reset dxp forced to 1.5v logic inputs forced to v cc or gnd auto-convert mode from stop bit to conversion complete (both channels) v cc , falling edge t a = 0? to +85? v cc input, disables a/d conversion, rising edge autoconvert mode, average measured over 4sec. logic inputs forced to v cc or gnd. conditions ? 160 address pin bias current v 0.7 dxn source voltage ? 81012 80 100 120 remote-diode source current % -25 25 conversion rate timing error ms 94 125 156 conversion time ? 120 180 35 70 average operating supply current -2 2 bits 8 temperature resolution (note 1) ? 5 standby supply current 310 mv 50 por threshold hysteresis v 1.0 1.7 2.5 power-on reset threshold ? -3 3 initial temperature error, local diode (note 2) v 3.0 5.5 supply voltage range v 2.60 2.80 2.95 undervoltage lockout threshold mv 50 undervoltage lockout hysteresis units min typ max parameter t r = +60? to +100? t r = -55? to +125? (note 4) -3 3 ? -5 5 temperature error, remote diode (notes 2, 3) including long-term drift -2.5 2.5 ? -3.5 3.5 temperature error, local diode (notes 1, 2) 0.25 conv/sec 2.0 conv/sec t a = +60? to +100? t a = 0? to +85? high level low level adc and power supply smbus static hardware or software standby, smbclk at 10khz
max1619 remote/local temperature sensor with dual- alarm outputs and smbus serial interface _______________________________________________________________________________________ 3 electrical characteristics (continued) (v cc = +3.3v, t a = 0? to +85? , configuration byte = xch, unless otherwise noted.) stby , smbclk, smbdata; v cc = 3v to 5.5v t high , 90% to 90% points t low , 10% to 10% points (note 5) smbclk, smbdata logic inputs forced to v cc or gnd alert, overt, forced to 5.5v stby , smbclk, smbdata; v cc = 3v to 5.5v alert, overt , smbdata forced to 0.4v conditions ? 4 smbclk clock high time ? 4.7 smbclk clock low time khz dc 100 smbus clock frequency pf 5 smbus input capacitance ? -1 1 logic input current ? 1 alert, overt output high leakage current v 2.2 logic input high voltage v 0.8 logic input low voltage ma 6 logic output low sink current units min typ max parameter t su:dat , 10% or 90% of smbdata to 10% of smbclk t su:sto , 90% of smbclk to 10% of smbdata t hd:sta , 10% of smbdata to 90% of smbclk t su:sta , 90% to 90% points ns 250 smbus data valid to smbclk rising-edge time ? 4 smbus stop-condition setup time ? 4 smbus start-condition hold time ns 500 smbus repeated start-condition setup time ? 4.7 smbus start-condition setup time t hd:dat (note 6) ? 0 smbus data-hold time master clocking in data ? 1 smbclk falling edge to smbus data-valid time smbus interface electrical characteristics (v cc = +3.3v, t a = -55? to +125? , configuration byte = xch, unless otherwise noted.) (note 4) conditions monotonicity guaranteed t a = +60? to +100? bits 8 temperature resolution (note 1) -2 2 t r = +60? to +100? t a = -55? to +125? ? -3 3 initial temperature error, local diode (note 2) v 3.0 5.5 supply voltage range from stop bit to conversion complete (both channels) autoconvert mode ms 94 125 156 conversion time % -25 25 conversion rate timing error -3 3 t r = -55? to +125? ? units min typ max -5 5 parameter temperature error, remote diode (notes 2, 3) adc and power supply
0 6 3 9 12 50 5k 500k 50k 5m 500 50m temperature error vs. power-supply noise frequency max1619-03 frequency (hz) temperature error (?) v in = square wave applied to v cc with no 0.1 m f v cc capacitor v in = 250mvp-p remote diode v in = 100mvp-p local diode v in = 100mvp-p remote diode -20 -10 -15 0 -5 10 5 20 15 temperature error vs. pc board resistance max1619-01 leakage resistance (m w ) temperature error (?) 1 10 100 path = dxp to gnd path = dxp to v cc (5v) -2 -1 0 1 2 -50 50 100 0 150 temperature error vs. remote-diode temperature max1619-02 temperature (?) temperature error (?) motorola mmbt3904 zetex fmmt3904 random samples __________________________________________typical operating characteristics (t a = +25?, unless otherwise noted.) max1619 remote/local temperature sensor with dual- alarm outputs and smbus serial interface 4 _______________________________________________________________________________________ electrical characteristics (continued) (v cc = +3.3v, t a = -55? to +125? , configuration byte = xch, unless otherwise noted.) (note 4) note 1: guaranteed but not 100% tested. note 2: quantization error is not included in specifications for temperature accuracy. for example, if the max1619 device tempera- ture is exactly +66.7?, the adc may report +66?, +67?, or +68? (due to the quantization error plus the +1/2? offset used for rounding up) and still be within the guaranteed ?? error limits for the +60? to +100? temperature range (table 2). note 3: a remote diode is any diode-connected transistor from table 1. t r is the junction temperature of the remote diode. see remote diode selection for remote diode forward voltage requirements. note 4: specifications from -55? to +125? are guaranteed by design, not production tested. note 5: the smbus logic block is a static design that works with clock frequencies down to dc. while slow operation is possible, it violates the 10khz minimum clock frequency and smbus specifications, and may monopolize the bus. note 6: note that a transition must internally provide at least a hold time in order to bridge the undefined region (300ns max) of smbclk? falling edge. conditions units min typ max parameter stby , smbclk, smbdata 2.2 logic input high voltage v 2.4 stby , smbclk, smbdata; v cc = 3v to 5.5v v 0.8 logic input low voltage alert, overt forced to 5.5v ? 1 alert , overt output high leakage current logic inputs forced to v cc or gnd ? -2 2 logic input current v cc = 3v v cc = 5.5v alert, overt , smbdata forced to 0.4v ma 6 logic output low sink current smbus interface
max1619 remote/local temperature sensor with dual- alarm outputs and smbus serial interface _______________________________________________________________________________________ 5 0 2 4 8 6 10 temperature error vs. common-mode noise frequency max1619-04 frequency (mhz) temperature error (?) 0.1 10 100 1 v in = 100mvp-p v in = square wave ac-coupled to dxn v in = 50mvp-p v in = 25mvp-p 0 10 20 04060 80 20 100 temperature error vs. dxp?xn capacitance max1619-07 dxp?xn capacitance (nf) temperature error (?) v cc = 5v 0 100 400 200 300 500 01 0.0625 4 0.25 2 0.125 0.5 8 operating supply current vs. conversion rate max1619-10 conversion rate (hz) supply current ( m a) v cc = 5v averaged measurements 0 10 20 30 40 50 1 100 10 1000 standby supply current vs. clock frequency max1619-08 smbclk frequency (khz) supply current ( m a) v cc = 5v v cc = 3.3v 0 3 60 6 20 100 03 14 25 standby supply current vs. supply voltage max1619-09 supply voltage (v) supply current ( m a) add0, add1 = gnd add0, add1 = high-z 0 25 100 50 75 125 -2 8 04 2610 internal diode response to thermal shock max1619-11 time (sec) temperature (?) 16-qsop immersed in +115? fluorinert bath typical operating characteristics (continued) (t a = +25?, unless otherwise noted.)
max1619 remote/local temperature sensor with dual- alarm outputs and smbus serial interface 6 _______________________________________________________________________________________ pin description detailed description the max1619 is a temperature sensor designed to work in conjunction with an external microcontroller (?) or other intelligence in thermostatic, process-control, or monitoring applications. the ? is typically a power- management or keyboard controller, generating smbus serial commands either by ?it-banging?general-pur- pose input/output (gpio) pins or through a dedicated smbus interface block. essentially an 8-bit serial analog-to-digital converter (adc) with a sophisticated front end, the max1619 contains a switched current source, a multiplexer, an adc, an smbus interface, and associated control logic (figure 1). temperature data from the adc is loaded into two data registers (local and remote). the remote temperature data is automatically compared with data previously stored in four temperature-alarm threshold registers. one pair of alarm-threshold registers is used to provide hysteretic fan control; the other pair is used for alarm interrupt. the local temperature data is avail- able for monitoring. adc and multiplexer the adc is an averaging type that integrates over a 60ms period (each channel, typical) with excellent noise rejection. the multiplexer automatically steers bias currents through the remote and local diodes, measures their forward voltages, and computes their temperatures. both channels are automatically converted once the conversion process has started, either in free-running or single-shot mode. if one of the two channels is not used, the device still performs both measurements, and the user can simply ignore the results of the unused channel. the dxn input is biased at 0.65v above ground by an internal diode to set up the analog-to-digital (a/d) inputs for a differential measurement. the worst-case dxp?xn differential input voltage range is 0.25v to 0.95v. excess resistance in series with the remote diode caus- es about +1/2? error per ohm. likewise, 200? of off- set voltage forced on dxp?xn causes about 1? error. smbus serial-data input/output, open drain smbdata 12 smbus serial-clock input smbclk 14 hardware standby input. temperature and comparison threshold data are retained in standby mode. low = standby mode, high = operate mode. stby 15 smbus address select pin (table 8). add0 and add1 are sampled upon power-up. excess capacitance (>50pf) at the address pins when floating may cause address-recognition problems. add1 6 ground gnd 7, 8 smbus slave address select pin add0 10 smbus alert (interrupt) output, open drain alert 11 combined current sink and a/d negative input. dxn is normally internally biased to a diode voltage above ground. dxn 4 combined current source and a/d positive input for remote-diode channel. do not leave dxp floating; connect dxp to dxn if no remote diode is used. place a 2200pf capacitor between dxp and dxn for noise filtering. dxp 3 pin supply voltage input, 3v to 5.5v. bypass to gnd with a 0.1? capacitor. a 200 series resistor is recom- mended but not required for additional noise filtering. v cc 1 function name overtemperature alarm output, open drain. this is an unlatched alarm output that responds only to the remote diode temperature. overt 9 not internally connected. connect to gnd to act against leakage paths from v cc to dxp. gnd 2 no connection. not internally connected. may be used for pc board trace routing. n.c. 5, 13, 16
max1619 remote/local temperature sensor with dual- alarm outputs and smbus serial interface _______________________________________________________________________________________ 7 figure 1. functional diagram remote mux local remote temperature data register high-temperature threshold (remote t high ) low-temperature threshold (remote t low ) digital comparator (remote) local temperature data register high-temperature threshold (remote t max ) hysteresis threshold (remote t hyst ) digital comparator (remote overtemp) command byte (index) register smbdata smbclk address decoder read write control logic smbus add1 add0 stby status byte register configuration byte register conversion rate register alert response address register selected via slave add = 0001 100 adc + diode fault dxp dxn gnd v cc - + - + - 8 8 8 8 8 88 2 7 alert overt qs r q s r pol max1619
a/d conversion sequence if a start command is written (or generated automatical- ly in the free-running auto-convert mode), both channels are converted, and the results of both measurements are available after the end of conversion. a busy status bit in the status byte shows that the device is actually performing a new conversion; however, even if the adc is busy, the results of the previous conversion are always available. remote-diode selection temperature accuracy depends on having a good-qual- ity, diode-connected small-signal transistor. accuracy has been experimentally verified for all the devices list- ed in table 1. the max1619 can also directly measure the die temperature of cpus and other integrated cir- cuits having on-board temperature-sensing diodes. 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 must be greater than 0.25v at 10?; check to ensure this is true at the highest expected temperature. the forward voltage must be less than 0.95v at 100?; check to ensure this is true at the lowest expected temperature. large power transistors don? work. also, ensure that the base resistance is less than 100 . tight specifications for forward-current gain (+50 to +150, for example) indicate that the manufacturer has good process controls and that the devices have consistent v be characteristics. for heatsink mounting, the 500-32bt02-000 thermal sensor from fenwal electronics is a good choice. this device consists of a diode-connected transistor, an aluminum plate with screw hole, and twisted-pair cable (fenwal inc., milford, ma, 508-478-6000). thermal mass and self-heating thermal mass can seriously degrade the max1619? effective accuracy. the thermal time constant of the qsop-16 package is about 4sec in still air. to settle to within +1? after a sudden +100? change, the max1619 junction temperature requires about five time constants. the use of smaller packages for remote sen- sors, such as sot23s, improves the situation. take care to account for thermal gradients between the heat source and the sensor, and ensure that stray air cur- rents 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 the local diode, the worst-case error occurs when auto-converting at the fastest rate and simultaneously sinking maximum cur- rent at the alert and overt outputs. for example, at an 8hz rate and with alert and overt each sinking 1ma, the typical power dissipation is: (v cc )(450?) + 2(0.4v)(1ma) package q ja is about 120?/w, so with v cc = 5v and no copper pc board heatsinking, the resulting tempera- ture rise is: ? t = 3.1mw(120?/w) = 0.36? even with these contrived circumstances, it is difficult to introduce significant self-heating errors. adc noise filtering the adc is an integrating type with inherently good noise rejection, especially of low-frequency signals such as 60hz/120hz power-supply hum. micropower opera- tion places constraints on high-frequency noise rejection; therefore, careful pc board layout and proper external noise filtering are required for high-accuracy remote measurements in electrically noisy environments. high-frequency emi is best filtered at dxp and dxn with an external 2200pf capacitor. this value can be increased to about 3300pf (max), including cable capacitance. capacitance higher than 3300pf intro- duces errors due to the rise time of the switched cur- rent source. nearly all noise sources tested cause the adc measure- ments to be higher than the actual temperature, typically by +1? to +10?, depending on the frequency and amplitude (see typical operating characteristics ). max1619 remote/local temperature sensor with dual- alarm outputs and smbus serial interface 8 _______________________________________________________________________________________ cmpt3904 central semiconductor (usa) mmbt3904 fairchild semiconductor (usa) sst3904 rohm semiconductor (japan) fmmt3904ct-nd zetex (england) manufacturer model number smbt3904 siemens (germany) table 1. remote-sensor transistor manufacturers note: transistors must be diode-connected (base shorted to collector). mmbt3904 motorola (usa)
pc board layout 1) place the max1619 as close as practical to the remote diode. in a noisy environment, such as a computer motherboard, this distance can be 4 inch- es to 8 inches (typical) or more as long as the worst noise sources (such as crts, clock generators, memory buses, and isa/pci buses) are avoided. 2) do not route the dxp?xn lines next to the deflec- tion coils of a crt. also, do not route the traces across a fast memory bus, which can easily intro- duce +30? error, even with good filtering. otherwise, most noise sources are fairly benign. 3) route the dxp and dxn traces in parallel and in close proximity to each other, away from any high- voltage traces such as +12v dc . leakage currents from pc board contamination must be dealt with carefully, since a 10m leakage path from dxp to ground causes about +1? error. 4) connect guard traces to gnd on either side of the dxp?xn traces (figure 2). with guard traces in place, routing near high-voltage traces is no longer an issue. 5) route through as few vias and crossunders as possi- ble to minimize copper/solder thermocouple effects. 6) when introducing a thermocouple, make sure that both the dxp and the dxn paths have matching thermocouples. in general, pc board-induced ther- mocouples are not a serious problem. a copper-sol- der thermocouple exhibits 3?/?, and it takes about 200? of voltage error at dxp?xn to cause a +1? measurement error. so, most parasitic ther- mocouple errors are swamped out. 7) use wide traces. narrow ones are more inductive and tend to pick up radiated noise. the 10 mil widths and spacings recommended in figure 2 aren? absolutely necessary (as they offer only a minor improvement in leakage and noise), but try to use them where practical. 8) keep in mind that copper can? be used as an emi shield, and only ferrous 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. pc board layout checklist place the max1619 close to a remote diode. keep traces away from high voltages (+12v bus). keep traces away from fast data buses and crts. use recommended trace widths and spacings. place a ground plane under the traces. use guard traces flanking dxp and dxn and con- necting to gnd. place the noise filter and the 0.1? v cc bypass capacitors close to the max1619. add a 200 resistor in series with v cc for best noise filtering (see typical operating circuit ). twisted pair and shielded cables for remote-sensor distances longer than 8 inches, or in particularly noisy environments, a twisted pair is recom- mended. its practical length is 6 feet to 12 feet (typical) before noise becomes a problem, as tested in a noisy electronics laboratory. for longer distances, the best solution is a shielded twisted pair like that used for audio microphones. for example, the belden 8451 works well in a noisy environment for distances up to 100 feet. connect the twisted pair to dxp and dxn and the shield to gnd, and leave the shield? remote end unterminated. excess capacitance at dx_ limits practical remote sen- sor distances (see typical operating characteristics ). for very long cable runs, the cable? 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; 1 series resistance introduces about +1/2? error. low-power standby mode standby mode disables the adc and reduces the sup- ply-current drain to 3? (typical). enter standby mode by forcing the stby pin low or via the run/stop bit in the configuration byte register. hardware and software standby modes behave almost identically: all data is retained in memory, and the smb interface is alive and listening for reads and writes. the only difference is that in hardware standby mode, the one-shot command does not initiate a conversion. standby mode is not a shutdown mode. with activity on the smbus, extra supply current is drawn (see typical operating characteristics ). in software standby mode, max1619 remote/local temperature sensor with dual- alarm outputs and smbus serial interface _______________________________________________________________________________________ 9 minimum 10 mils 10 mils 10 mils 10 mils gnd dxn dxp gnd figure 2. recommended dxp/dxn pc traces
the max1619 can be forced to perform a/d conversions via the one-shot command, despite the run/stop bit being high. activate hardware standby mode by forcing the stby pin low. in a notebook computer, this line may be con- nected to the system sustat# suspend-state signal. the stby pin low state overrides any software conversion command. if a hardware or software standby command is received while a conversion is in progress, the conver- sion cycle is truncated, and the data from that conversion is not latched into either temperature reading register. the previous data is not changed and remains available. the overt output continues to function in both hard- ware and software standby modes. if the overtemp lim- its are adjusted while in standby mode, the digital comparator checks the new values and puts the overt pin in the correct state based on the last valid adc con- version. the last valid adc conversion may include a conversion performed using the one-shot command. supply-current drain during the 125ms conversion peri- od is always about 450?. slowing down the conversion rate reduces the average supply current (see typical operating characteristics ). between conversions, the instantaneous supply current is about 25? due to the current consumed by the conversion rate timer. in standby mode, supply current drops to about 3a. at very low supply voltages (under the power-on-reset threshold), the supply current is higher due to the address pin bias currents. it can be as high as 100?, depending on add0 and add1 settings. smbus digital interface from a software perspective, the max1619 appears as a set of byte-wide registers that contain temperature data, alarm threshold values, or control bits. a standard smbus 2-wire serial interface is used to read tempera- ture data and write control bits and alarm threshold data. each a/d channel within the device responds to the same smbus slave address for normal reads and writes. the max1619 employs four standard smbus protocols: write byte, read byte, send byte, and receive byte (figure 3). the shorter receive byte protocol allows quicker transfers, provided that the correct data register was previously selected by a read byte instruction. use caution with the shorter protocols in multi-master sys- max1619 remote/local temperature sensor with dual- alarm outputs and smbus serial interface 10 ______________________________________________________________________________________ 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: equivalent 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 s command 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 ack 7 bits address wr 8 bits command ack p s 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 figure 3. smbus protocols
tems, since a second master could overwrite the com- mand byte without informing the first master. the temperature data format is 7 bits plus sign in two? complement form for each channel, with each data bit rep- resenting 1? (table 2), transmitted msb first. measure- ments are offset by +1/2? to minimize internal rounding errors; for example, +99.6? is reported as +100?. alarm threshold registers two registers store alert threshold limits, with high- temperature (t high ) and low-temperature (t low ) reg- isters for the remote a/d channel. there are no comparison registers for the local a/d channel. if either measured temperature equals or exceeds the corre- sponding alarm threshold value, an alert interrupt is asserted. the power-on-reset (por) state of the t high register is full scale (0111 1111, or +127?). the por state of the t low register is 1100 1001 or -55?. two additional alarm threshold registers control the overt output (see overt alarm output section), t max and t hyst . the por state of t max is +100?, and t hyst is +95?. o o v v e e r r t t alarm output for fan control the overt output is an unlatched open-drain output that behaves as a thermostat to control a fan (figure 4). when using the smbus interface, the polarity of the overt pin (active-low at por) can be inverted via bit 5 in the config- uration byte. overt ? current state can be read in the status byte. overt can also be used to control a fan without system intervention. overt goes low when the remote tempera- ture rises above t max and won? go high again until the temperature drops below t hyst . the power-up default settings for t max and t hyst (+100? and +95?, respectively) allow the max1619 to be used in stand- alone thermostat applications where connection to an smbus serial bus isn? required. diode fault alarm there is a continuity fault detector at dxp that detects whether the remote diode has an open-circuit condi- tion. at the beginning of each conversion, the diode fault is checked, and the status byte is updated. this fault detector is a simple voltage detector; if dxp rises above v cc - 1v (typical) due to the diode current source, a fault is detected. note that the diode fault isn? checked until a conversion is initiated, so immedi- ately after power-on reset the status byte indicates no fault is present, even if the diode path is broken. max1619 remote/local temperature sensor with dual- alarm outputs and smbus serial interface ______________________________________________________________________________________ 11 digital output data bits 0 111 1111 +127 +127.00 0 111 1111 0 111 1110 +126 +126.00 +127 +126.50 0 001 1001 0 000 0001 +1 +0.50 0 000 0000 0 000 0000 0 0.00 rounded temp. (?) temp. (?) 0 +0.25 +25 +25.25 0 000 0000 0 000 0000 0 -0.50 1 111 1111 1 111 1111 -1 -1.00 -1 -0.75 1 110 0111 1 110 0111 -25 -25.50 1 100 1001 1 100 1001 -55 -55.00 0 -0.25 -55 -54.75 -25 -25.00 1 011 1111 1 011 1111 -65 -70.00 -65 -65.00 table 2. data format (two? complement) sign msb lsb 0 111 1111 +127 +130.00 max1619 smbclk add0 add1 stby v cc pgnd +12v gnd dxp dxn +3v to +5.5v smbus serial interface (to host) 2n3904 smbdata alert overt figure 4. fan control application
if the remote channel is shorted (dxp to dxn or dxp to gnd), the adc reads 0000 0000 so as not to trip either the t high or t low alarms at their por settings. in applications that are never subjected to 0? in normal operation, a 0000 0000 result can be checked to indi- cate a fault condition in which dxp is accidentally short circuited. similarly, if dxp is short circuited to v cc , the adc reads +127? for both remote and local channels, and the alert and overt outputs are activated. a a l l e e r r t t interrupts the alert interrupt output signal is latched and can only be cleared by reading the alert response address. interrupts are generated in response to t high and t low comparisons and when the remote diode is disconnect- ed (for continuity fault detection). the interrupt does not halt automatic conversions; new temperature data con- tinues to be available over the smbus interface after alert is asserted. the interrupt output pin is open-drain so that devices can share a common interrupt line. the interrupt rate can never exceed the conversion rate. the interface responds to the smbus alert response address, an interrupt pointer return-address feature (see alert response address section). prior to taking corrective action, always check to ensure that an inter- rupt is valid by reading the current temperature. to prevent reoccurring interrupts, the max1619 asserts alert only once per crossing of a given temperature threshold. to enable a new interrupt, the value in the limit register that triggered the interrupt must be rewrit- ten. note that other interrupt conditions can be caused by crossing the opposite temperature threshold, or a diode fault can still cause an interrupt. example: the remote temperature reading crosses t high , activating alert . the host responds to the interrupt and reads the alert response address, clear- ing the interrupt. the system may also read the status byte at this time. the condition that caused the interrupt persists, but no new alert interrupt is issued. finally, the host writes a new value to t high . this enables the device to generate a new t high interrupt if the alert condition still exists. alert response address the smbus alert response interrupt pointer provides quick fault identification for simple slave devices that lack the complex, expensive logic needed to be a bus master. upon receiving an alert interrupt signal, the host mas- ter can broadcast a receive byte transmission to the alert response slave address (0001 100). then any slave device that generated an interrupt attempts to identify itself by putting its own address on the bus (table 3). 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 arbitration rules apply, and the device with the lower address code wins. the losing device does not gener- ate an acknowledge and continues to hold the alert line low until serviced (implies that the host interrupt input is level-sensitive). successful reading of the alert response address clears the interrupt latch. command byte functions the 8-bit command byte register (table 4) is the master index that points to the other registers within the max1619. the register? por state is 0000 0001 so that a receive byte transmission (a protocol that lacks the command byte) that occurs immediately after por returns the current remote temperature data. the one-shot command immediately forces a new conver- sion cycle to begin. in software standby mode (run/stop bit = high), a new conversion is begun, after which the device returns to standby mode. if a conversion is in progress when a one-shot command is received, the command is ignored. if a one-shot command is received in auto-convert mode (run/stop bit = low) between con- versions, a new conversion begins, the conversion rate timer is reset, and the next automatic conversion takes place after a full delay elapses. configuration byte functions the configuration byte register (table 5) is used to mask (disable) interrupts, to put the device in software standby mode, to change the polarity of the overt output, and to enable the write-once protection. the lowest two bits are internally set to zeros, making them ?on? care?bits. this register? contents can be read back over the serial interface. max1619 remote/local temperature sensor with dual- alarm outputs and smbus serial interface 12 ______________________________________________________________________________________ i 2 c is a trademark of philips corp. table 3. read format for alert response address (0001100) add6 6 provide the current max1619 slave address function add5 5 add4 4 add3 3 add2 2 add1 1 add7 7 (msb) 1 0 (lsb) logic 1 bit name
max1619 remote/local temperature sensor with dual- alarm outputs and smbus serial interface ______________________________________________________________________________________ 13 table 4. command-byte bit assignments * if the device is in hardware standby mode at por, both temperature registers read 0?. read remote temperature: returns latest temperature rrte 01h 00h command 0000 0000* 0000 0000* por state read configuration byte rcl 03h 02h 0000 1100 n/a read status byte (flags, busy signal) rsl read remote t max limit rrtm 10h read local temperature: returns latest temperature rlts 04h 01100100 0000 0010 read remote t high limit rrhi 07h 11h 0111 1111 01011111 read remote t hyst limit rrth read conversion rate byte register rcra write configuration byte wca 09h 08h n/a 1100 1001 function write remote t max limit wrtm 12h 0ah n/a n/a write conversion rate byte wcrw write remote t high limit wrha 0dh read remote t low limit rrls 13h n/a n/a one-shot command osht 0fh 0eh n/a n/a write remote t low limit wrln write remote t hyst limit wrth run/ stop 6 0 0 por state standby mode control bit. if high, the device immediately stops converting and enters standby mode. if low, the device converts in either one-shot or timer mode. masks all alert interrupts when high. function pol 5 0 determines the polarity of the overt output: 0 = active low (low when overtemp) 1 = active high mask 7 (msb) bit name table 5. configuration-byte bit assignments write address wadd fdh fch n/a n/a read device id code dev id ffh feh 0000 0100 0100 1101 read manufacturer id code mfg id write software por spor prot 4 0 when asserted high, locks out all subsequent writes to: [] configuration register bits 6, 5, 4, 3, 2 (run/stop, pol, prot, id1, id2) [] t max register [] t hyst register [] conversion rate register [] diode current id1 3 1 reduces the diode current by 5? when set low. id2 2 1 reduces the diode current by 2.5? when set low. rfu 1? 0 reserved for future use.
max1619 remote/local temperature sensor with dual- alarm outputs and smbus serial interface 14 ______________________________________________________________________________________ write-once protection write-once protection allows the host bios code to configure the max1619 in a particular way, and then protect that configuration against data corruption in the host that might cause spurious writes to the max1619. in particular, write protection allows a foolproof over- temperature override that forces the fan on 100% via overt independent of the host system. the write-pro- tection bit (bit 4), once set high, can? be reset to low except by a hardware power-on reset. a spor (soft- ware por) will not reset this bit. status byte functions the status byte register (table 6) indicates which (if any) temperature thresholds have been exceeded. this byte also indicates whether or not the adc is converting and whether there is an open circuit in the remote diode dxp?xn path. the status byte is cleared by any suc- cessful read of the status byte, unless the fault persists. the status of bit1 ( over ) follows the state of overt exactly. note that the alert interrupt latch is not auto- matically cleared when the status flag bit is cleared. when autoconverting, if the t high and t low limits are close together, it? possible for both high-temp and low- temp status bits to be set, depending on the amount of time between status read operations (especially when converting at the fastest rate). in these circumstances, it? 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. conversion rate byte the conversion rate register (table 7) programs the time interval between conversions in free-running autoconvert mode. this variable rate control reduces the supply cur- rent in portable-equipment applications. the conversion rate byte? por state is 02h (0.25hz). the max1619 looks only at the 3 lsb bits of this register, so the upper 5 bits are ?on? care?bits, which should be set to zero. the conversion rate tolerance is ?5% at any rate setting. valid a/d conversion results for both channels are avail- able one total conversion period (125ms nominal, 156ms maximum) after initiating a conversion, whether conver- sion is initiated via the run/stop bit, hardware stby pin, one-shot command, or initial power-up. changing the conversion rate can also affect the delay until new results are available (table 8). manufacturer and device id codes two rom registers provide manufacturer and device id codes (table 4). reading the manufacturer id returns 4dh, which is the ascii code ??(for maxim). reading the device id returns 04h, indicating a max1619 device. if read word 16-bit smbus protocol is employed (rather than the 8-bit read byte), the least significant byte contains the data and the most significant byte con- tains 00h in both cases. slave addresses the max1619 appears to the smbus as one device having a common address for both adc channels. the device address can initially be set to one of nine differ- ent values by pin-strapping add0 and add1 so that more than one max1619 can reside on the same bus without address conflicts (table 9). table 6. status-byte bit assignments * the high and low temperature alarm flags stay high until cleared by por or until status register is read. rfu 6 reserved for future use. a high indicates that the adc is busy converting. function rfu 5 reserved for future use. rhigh* 4 a high indicates that the remote high- temperature alarm has activated. rlow* 3 a high indicates that the remote low- temperature alarm has activated. open* 2 a high indicates a remote-diode conti- nuity (open-circuit) fault. over 1 busy 7 (msb) this bit follows the state of the overt pin exactly, in real time (unlatched). rfu 0 (lsb) reserved for future use. bit name table 7. conversion-frequency control byte 0.125 01h 33 30 average supply current (? typ, at v cc = 3.3v) 0.25 02h 35 0.5 03h 48 1 04h 70 2 05h 128 4 06h 0.0625 00h 225 8 07h 425 rfu 08h to ffh data conversion frequency (hz)
the address pin states are checked at por and spor only, and the address data stays latched to reduce qui- escent supply current due to the bias current needed for high-z state detection. a new device address can be written using the write address command fdh. the max1619 also responds to the smbus alert response slave address (see the alert response address section). por and uvlo the max1619 has a volatile memory. to prevent ambig- uous 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 1.7v (typical, see electrical characteristics table). when power is first applied and v cc rises above 1.75v (typical), the logic blocks begin operating, although reads and writes at v cc levels below 3v are not recommended. a second v cc comparator, the adc uvlo comparator, prevents the adc from converting until there is sufficient headroom (v cc = 2.8v typical). the spor software por command can force a power-on reset of the max1619 registers via the serial interface. use the send byte protocol with command = fch. this is most commonly used to reconfigure the slave address of the max1619 ?n the fly,?where external hardware has forced new states at the add0 and add1 address pins prior to the software por. the new address takes effect less than 100? after the spor transmission stop condition. power-up defaults: interrupt latch is cleared. address select pins are sampled. adc begins auto-converting at a 0.25hz rate. command byte is set to 01h to facilitate quick remote receive byte queries. t high and t low registers are set to +127? and -55?, respectively. t max and t hyst are set to +100? and +95?, respectively. overt polarity is active low. max1619 remote/local temperature sensor with dual- alarm outputs and smbus serial interface ______________________________________________________________________________________ 15 table 8. rlts and rrte temperature register update timing chart n/a (0.25hz) new conversion frequency (changed via write to wcrw) power-on reset autoconvert operating mode conversion initiated by: 156ms max time until rlts and rrte are updated 156ms max n/a one-shot command, while idling between automatic conversions autoconvert when current conversion is complete (1-shot is ignored) 20sec n/a 0.0625hz rate timer autoconvert one-shot command that occurs during a conversion autoconvert 10sec 5sec 0.125hz 0.25hz rate timer autoconvert 2.5sec 1.25sec 0.5hz 1hz rate timer autoconvert rate timer autoconvert rate timer autoconvert 625ms 312.5ms 2hz 4hz rate timer autoconvert 237.5ms 156ms 8hz n/a stby pin hardware standby rate timer autoconvert rate timer autoconvert 156ms 156ms n/a n/a one-shot command software standby run/stop bit software standby table 9. por slave address decoding (add0 and add1) note: high-z means that the pin is left unconnected and floating. 0011 001 high-z gnd 0011 000 address 0101 001 gnd high-z 0011 010 v cc gnd 0101 011 v cc high-z 0101 010 1001 101 high-z v cc 1001 100 gnd gnd gnd v cc high-z high-z 1001 110 v cc v cc add0 add1
max1619 remote/local temperature sensor with dual- alarm outputs and smbus serial interface 16 ______________________________________________________________________________________ figure 6. smbus read timing diagram figure 5. smbus write timing diagram 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 h i j smbdata t su:sta t hd:sta t low t high t su:dat t su:sto t buf k 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 = acknowledge clock pulse j = stop condition k = new start condition 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 = slave pulls smbdata line low j = acknowledge clocked into master k = acknowledge clock pulse l = stop condition, data executed by slave m = new start condition
max1619 remote/local temperature sensor with dual- alarm outputs and smbus serial interface ______________________________________________________________________________________ 17 listing 1. pseudocode example
max1619 remote/local temperature sensor with dual- alarm outputs and smbus serial interface 18 ______________________________________________________________________________________ listing 1. pseudocode example (continued)
max1619 remote/local temperature sensor with dual- alarm outputs and smbus serial interface ______________________________________________________________________________________ 19 listing 1. pseudocode example (continued) programming example: clock-throttling control for cpus listing 1 gives an untested example of pseudocode for proportional temperature control of intel mobile cpus through a power-management microcontroller. this program consists of two main parts: an initialization rou- tine and an interrupt handler. the initialization routine checks for smbus communications problems and sets up the max1619 configuration and conversion rate. the interrupt handler responds to alert signals by reading the current temperature and setting a cpu clock duty factor proportional to that temperature. the relationship between clock duty and temperature is fixed in a look- up table contained in the microcontroller code. note: thermal management decisions should be made based on the latest external temperature obtained from the max1619 rather than the value of the status byte. the max1619 responds very quickly to changes in its environment due to its sensitivity. high and low alarm conditions can exist at the same time in the status byte due to the max1619 correctly reporting environmental changes around it. chip information transistor count: 11,487
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. 20 __________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 (408) 737-7600 1999 maxim integrated products printed usa is a registered trademark of maxim integrated products. max1619 remote/local temperature sensor with dual- alarm outputs and smbus serial interface package information qsop.eps

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