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general description the max6646/max6647/max6649 are precise, two-channel digital temperature sensors. the devices accu- rately measure the temperature of their own die and a remote pn junction, and report the temperature in digital form using a 2-wire serial interface. the remote pn junc- tion is typically the emitter-base junction of a common- collector pnp on a cpu, fpga, or asic. the 2-wire serial interface accepts standard system man- agement bus (smbus) write byte, read byte, send byte, and receive byte commands to read the temperature data and to program the alarm thresholds. to enhance system reliability, the max6646/max6647/max6649 include an smbus timeout. a fault queue prevents the alert and overt outputs from setting until a fault has been detected one, two, or three consecutive times (programmable). the max6646/max6647/max6649 provide two system alarms: alert and overt . alert asserts when any of four temperature conditions are violated: local overtem-perature, remote overtemperature, local undertempera- ture, or remote undertemperature. overt asserts when the temperature rises above the value in either of the twoovert limit registers. the overt output can be used to activate a cooling fan, or to trigger a system shutdown. measurements can be done autonomously, at the pro- grammed conversion rate, or in a single-shot mode. the adjustable conversion rate allows optimizing supply cur- rent and temperature update rate to match system needs. remote accuracy is 1c maximum error between +60c and +145c with no calibration needed. the max6646/ max6647/max6649 operate from -55c to +125c, and measure temperatures between 0c and +145c. the max6646/max6647/max6649 are available in an 8-pin max ? package. applications features ? dual channel: measures remote and localtemperature ? 0.125? resolution ? high accuracy ?? (max) from +60? to +145?(remote), and ?? (max) from +60? to +100? (local) ? measures high-ideality thermal diodes up to +170? (apparent)+145? (real) ? two alarm outputs: alert and overt ? programmable under/overtemperature alarmtemperature thresholds ? programmable conversion rate ? smbus-compatible interface ? smbus timeout max6646/max6647/max6649 +145? precision smbus-compatible remote/ local sensors with overtemperature alarms ordering information v cc dxp dxn 10k each clock to fan driver or system shutdown 3.3v data interrupt to p 200 0.1 f sda sclk alert gnd 2200pf p max6646 max6647 max6649 overt typical operating circuit 19-2540; rev 4; 7/12 1 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 measured temp range max6646 mua+ -55c to +125c 8 max 0c to +145c max6647 mua+ -55c to +125c 8 max 0c to +145c max6649 mua+ -55c to +125c 8 max 0c to +145c selector guide, pin configurations, and functional diagram appear at end of data sheet. + denotes a lead(pb)-free/rohs-compliant package. max is a registered trademark of maxim integrated products, inc. graphics processorsdesktop computers notebook computers servers thin clientsworkstations test and measurement multichip modules downloaded from: http:///
max6646/max6647/max6649 +145? precision smbus-compatible remote/ local sensors with overtemperature alarms 2 absolute maximum ratings stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. these are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. all voltages referenced to gndv cc ...........................................................................-0.3v to +6v dxp.............................................................-0.3v to (v cc + 0.3v) dxn .......................................................................-0.3v to +0.8v sclk, sda, alert , overt .....................................-0.3v to +6v sda, alert , overt current .............................-1ma to +50ma dxn current .......................................................................1ma continuous power dissipation (t a = +70c) max (derate 4.8mw/c above +70c) ...................387.8mw esd protection (all pins, human body model) ................2000v junction temperature ......................................................+150c operating temperature range .........................-55c to +125c storage temperature range .............................-65c to +150c soldering temperature (reflow) .......................................+260c lead temperature (soldering, 10s) .................................+300c electrical characteristics(v cc = 3.0v to 5.5v, t a = -55c to +125c, unless otherwise specified. typical values are at v cc = 3.3v and t a = +100c.) (note 1) parameter symbol conditions min typ max units supply voltage v cc 3.0 5.5 v 0.125 c temperature resolution 11 bits v cc = 3.3v, t a = +100c, t rj = +60c to +145c -1.0 +1.0 v cc = 3.3v, t a = +60c to +100c, t rj = +25c to +145c -1.6 +1.6 remote temperature error v cc = 3.3v, t a = +0c to +100c, t rj = +0c to +145c -3.2 +3.2 c t a = +60c to +100c -2.0 +2.0 local temperature error v cc = 3.3v t a = 0c to +125c -3.0 +3.0 c supply sensitivity of temperature error 0.2 c/v undervoltage lockout (uvlo) threshold uvlo falling edge of v cc disables adc 2.4 2.7 2.95 v uvlo hysteresis 90 mv power-on-reset (por) threshold v cc falling edge 2.0 v por threshold hysteresis 90 mv standby supply current smbus static 3 12 a operating current during conversion 0.08 ma 0.25 conversions per second 40 80 average operating current 2 conversions per second 250 400 a conversion time t conv from stop bit to conversion completion 95 125 156 ms conversion time error -25 +25 % dxp and dxn leakage current standby mode 100 na high level 80 100 120 remote-diode source current i rj low level 8 10 12 a downloaded from: http:///
max6646/max6647/max6649 +145? precision smbus-compatible remote/ local sensors with overtemperature alarms 3 electrical characteristics (continued)(v cc = 3.0v to 5.5v, t a = -55c to +125c, unless otherwise specified. typical values are at v cc = 3.3v and t a = +100c.) (note 1) parameter symbol conditions min typ max units alert , oert i sink = 1ma 0.4 output low voltage i sink = 4ma 0.6 v output high leakage current v oh = 5.5v 1 a smbus-compatible interface (sclk and sda) logic input low voltage v il 0.8 v v cc = 3.0v 2.2 logic input high voltage v ih v cc = 5.5v 2.6 v input leakage current i leak v in = v gnd or v cc -1 +1 a output low-sink current i sink v ol = 0.6v 6 ma input capacitance c in 5 pf smbus-compatible timing (note 2) serial clock frequency f sclk (note 3) 100 khz bus free time between stop and start condition t buf 4.7 s repeat start condition setup time t su:sta 4.7 s start condition hold time t hd:sta 10% of sda to 90% of sclk 4 s stop condition setup time t su:sto 90% of sclk to 90% of sda 4 s clock low period t low 10% to 10% 4.7 s clock high period t high 90% to 90% 4 s data setup time t su:dat 250 ns data hold time t hd:dat (note 4) 250 ns receive sclk/sda rise time t r 1 s receive sclk/sda fall time t f 300 ns pulse width of spike suppressed t sp 0 50 ns smbus timeout t timeout sda low period for interface reset 25 37 55 ms note 1: all parameters tested at a single temperature. specifications over temperature are guaranteed by design. note 2: timing specifications guaranteed by design. note 3: the serial interface resets when sclk is low for more than t timeout . note 4: a transition must internally provide at least a hold time to bridge the undefined region (300ns max) of sclks falling edge. downloaded from: http:///
max6646/max6647/max6649 +145? precision smbus-compatible remote/ local sensors with overtemperature alarms typical operating characteristics (v cc = 3.3v, t a = +25c, unless otherwise noted.) max6649 toc01 supply voltage (v) standby supply current ( a) 5.0 4.5 4.0 3.5 3.0 3.5 4.0 4.5 5.02.5 3.0 5.5 standby supply current vs. supply voltage max6649 toc02 conversion rate (hz) operating supply current ( a) 4.00 2.00 1.00 0.50 0.25 0.13 100 200 300 400 0 0.63 operating supply current vs. conversion rate max6649 toc03 temperature ( c) temperature error ( c) 125 100 75 50 25 -1.5 -0.5 0 0.5 1.0 1.5 2.0 -2.0 0 remote temperature error vs. remote-diode temperature -1.0 t a = +85 c fairchild 2n3906 max6649 toc04 temperature ( c) temperature error ( c) 100 75 50 25 -1.5 -1.0 -0.5 0 0.5 1.0 -2.0 0 125 local temperature error vs. die temperature max6649 toc05 frequency (hz) temperature error ( c) 10k 1k 100 10 1 -1 0 1 2 3 4 5 -2 0.1 100k v cc = square wave applied to v cc with no bypass capacitor local error temperature error vs. power-supply noise frequency remote error max6649 toc06 frequency (hz) temperature error ( c) 10k 1k 100 10 -1 0 1 2 3 4 5 6 7 8 9 -2 1 100k local temperature error vs. common-mode noise frequency local error remote error v in = ac-coupled to dxn v in = 100mv p-p max6649 toc07 frequency (hz) temperature error ( c) 10k 1k 100 10 -0.5 0 0.5 1.0 1.5 2.0 -1.0 1 100k temperature error vs. differential-mode noise frequency max6649 toc08 dxp-dxn capacitance (nf) temperature error ( c) 10.000 1.000 -4 -3 -2 -1 0 1 -5 0.100 100.000 temperature error vs. dxp-dxn capacitance 4 downloaded from: http:///
max6646/max6647/max6649 +145? precision smbus-compatible remote/ local sensors with overtemperature alarms detailed description the max6646/max6647/max6649 are temperature sen-sors designed to work in conjunction with a microproces- sor or other intelligence in thermostatic, process-control, or monitoring applications. communication with the max6646/max6647/max6649 occurs through the smbus-compatible serial interface and dedicated alert and overtemperature outputs. alert asserts if the mea- sured local or remote temperature is greater than thesoftware-programmed alert high limit or less than the alert low limit in the max6649. alert also asserts, in the max6649, if the remote-sensing diode pins are short-ed or unconnected. the overtemperature alarm, overt , asserts if the software-programmed overt limit is exceeded. overt can be connected to fans, a system shutdown, a clock throttle control, or other thermal-man-agement circuitry. the max6646/max6647/max6649 convert temperatures to digital data either at a programmed rate or in single conversions. temperature data is represented as 11 bits, with the lsb equal to 0.125c. the main temperature data registers (at addresses 00h and 01h) are 8-bit regis- ters that represent the data as 8 bits with the full-scale reading indicating the diode fault status (table 1). the remaining 3 bits of temperature data are available in the extended registers at addresses 11h and 10h (table 2). adc and multiplexer the averaging adc integrates over a 60ms period(each channel, typically), with excellent noise rejection. the multiplexer automatically steers bias currents through the remote and local diodes. the adc and associated circuitry measure each diodes forward volt- age and compute the temperature based on this volt- age. both channels are automatically converted once the conversion process has started, either in free-run- ning or single-shot mode. if one of the two channels is not used, the device still performs both measurements, and the results of the unused channel can be ignored. if the remote-diode channel is unused, connect dxp to dxn rather than leaving the inputs open. pin description pin name function 1 v cc supply voltage input, 3v to 5.5v. bypass v cc to gnd with a 0.1f capacitor. a 200 series resistor is recommended but not required for additional noise filtering. 2 dxp combined remote-diode current source and a/d positive inp ut for remote-diode channel. do not leave dxp unconnected ; connect dxp to dxn if no remote diode is used. place a 2200pf capacitor between dxp and dxn for noise filtering. 3 dxn combined remote-diode current sink and a/d negative in put. dxn is internally connected to gr ound. 4 overt overtemperature alert/interrupt output, open drain. overt is logic low when the temperature is above the software-programmed threshold. 5 gnd ground 6 alert smbus alert (interrupt) output, open drain. alert asserts when temperature exceeds limits (high or low temperature). alert stays asserted until acknowledged by either reading the status register or by successfully responding to an alert response address, provided t hat the fault condition no longer exists. see the alert interrupts section. 7 sda smbus serial-data input/output, open drain 8 sclk smbus serial-clock input 5 temp ( c) digital output +145 1001 0001 +130 1000 0010 +128 1000 0000 +25 0001 1001 0 0000 0000 <0 0000 0000 diode fault (short or open) 1111 1111 table 1. main temperature data registerformat (00h, 01h) downloaded from: http:///
max6646/max6647/max6649 the dxp-dxn differential input voltage range is 0.25v to0.95v. excess resistance in series with the remote diode causes +0.5c (typ) error per ohm. remote temperature measurement range the max6646/max6647/max6649 measure remotetemperatures significantly above the +120c limit of many temperature sensors. external diode-connected transistors work well as temperature sensors up to approximately +145c, where accuracy begins to degrade. thermal diodes on some cpus have charac- teristics that produce apparent temperatures far above actual operating temperatures. the max6646/ max6647/max6649 measure apparent temperatures as high as +170c, as long as the actual temperature is less than +145c. a/d conversion sequence a conversion sequence consists of a local temperaturemeasurement and a remote temperature measurement. each time a conversion begins, whether initiated auto- matically in the free-running autonomous mode ( run = 0) or by writing a one-shot command, both channels areconverted, and the results of both measurements are available after the end of a conversion. a busy status bit in the status byte indicates that the device is performing a new conversion. the results of the previous conversion are always available, even if the adc is busy. low-power standby mode standby mode reduces the supply current to less than12a by disabling the adc and timing circuitry. enter standby mode by setting the run bit to 1 in the configu- ration byte register (table 6). all data is retained in mem-ory, and the smbus interface is active and listening for smbus commands. standby mode is not a shutdown mode. with activity on the smbus, the device draws more supply current (see typical operating characteristics ). in standby mode, the max6646/max6647/max6649 can beforced to perform a/d conversions through the one-shot command, regardless of the run bit status. if a standby command is received while a conversion isin progress, the conversion cycle is truncated, and the data from that conversion is not latched into a tempera- ture register. the previous data is not changed and remains available. supply-current drain during the 125ms conversion period is 250a (typ). slowing down the conversion rate reduces the average supply current (see typical operating characteristics ). between conversions, the conversion rate timer consumes 25a (typ) of supply current. instandby mode, supply current drops to 3a (typ). smbus digital interface from a software perspective, the max6646/max6647/ max6649 appear as a set of byte-wide registers that contain temperature data, alarm threshold values, andcontrol bits. a standard smbus-compatible 2-wire serial interface is used to read temperature data and write control bits and alarm threshold data. the max6646/max6647/max6649 employ four standard smbus protocols: write byte, read byte, send byte, and receive byte (figures 1, 2, and 3). the shorter receive byte protocol allows quicker transfers, provided that the correct data register was previously selected by a read byte instruction. use caution when using the shorter pro- tocols in multimaster systems, as a second master could overwrite the command byte without informing the first master. temperature data can be read from the read internal temperature (00h) and read external temperature (01h) registers. the temperature data format for these regis- ters is 8 bits for each channel, with the lsb representing 1c (table 1). the msb is transmitted first. an additional 3 bits can be read from the read external extended temperature register (10h), which extends the data to 11 bits and the resolution to 0.125c per lsb. an additional 3 bits can be read from the read internal extended temperature register (11h), which extends the data to 11 bits and the resolution to 0.125c per lsb (table 2). when a conversion is complete, the main temperature register and the extended temperature register are updated simultaneously. ensure that no conversions are completed between reading the main register and the extended register, so that both registers contain the result of the same conversion. +145? precision smbus-compatible remote/ local sensors with overtemperature alarms 6 fractional temp (?) digital output 0.000 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 2. extended resolution temperatureregister data format (10h, 11h) downloaded from: http:///
max6646/max6647/max6649 +145? precision smbus-compatible remote/ local sensors with overtemperature alarms to ensure valid extended data, read extended resolu-tion temperature data using one of the following approaches: 1) put the max6646/max6647/max6649 into standby mode by setting bit 6 of the configuration register to 1.initiate a one-shot conversion using command byte 0fh. when this conversion is complete, read the con- tents of the temperature data registers. 2) if the max6646/max6647/max6649 is in run mode, read the status byte. if the busy bit indicates that aconversion is in progress, wait until the conversion is complete (busy bit set to zero) before reading the temperature data. following a conversion comple- tion, immediately read the contents of the tempera- ture data registers. if no conversion is in progress, the data can be read within a few microseconds, which is a sufficiently short period of time to ensure that a new conversion cannot be completed until after the data has been read. smbclk a = start conditionb = msb of address clocked into slave c = lsb of address clocked into slave d = r/w bit clocked into slave ab cd e fg hi j smbdata t su:sta t hd:sta t low t high t su:dat t su:sto t buf lm k e = slave pulls smbdata line lowf = acknowledge bit clocked into master g = msb of data clocked into slave h = lsb of data clocked into slave i = master pulls data line lowj = acknowledge clocked into slave k = acknowledge clock pulse l = stop condition m = new start condition figure 2. smbus write timing diagram 7 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 whichregister you are writing to data byte: data goes into the registerset by the command byte (to set thresholds, configuration masks, and sampling rate) slave address: equiva-lent to chip-select line command byte: selectswhich register you are reading from slave address: repeateddue to change in data- flow direction data byte: reads fromthe register set by the command byte command byte: sends com-mand with no data, usually used for one-shot command data byte: reads data fromthe register commanded by the last read byte or write byte transmission; also used for smbus alert response return address s = start condition shaded = slave transmission p = stop condition /// = not acknowledged figure 1. smbus protocols s address wr ack command 7 bits 8 bits ack data 8 bits ack p 1 s address wr ack command ack s address rd ack data /// p 8 bits 7 bits 8 bits 7 bits s address wr ack command ack p 7 bits 8 bits s address rd ack data /// p 8 bits 7 bits downloaded from: http:///
max6646/max6647/max6649 +145? precision smbus-compatible remote/ local sensors with overtemperature alarms 8 alarm threshold registers four registers store alert threshold valuesone high- temperature (t high ) and one low-temperature (t low ) register each for the local and remote channels. if eithermeasured temperature equals or exceeds the corre- sponding alert threshold value, the alert interrupt asserts.the max6646/max6647 local (internal) alert t high register por state is 0101 0101, or +85c, while theremote (external) alert t high register por state is 0101 1111, or +95c.the max6649 por state of bothalert t high registers is 0101 0101, or +85c. the por state of the local and remote t low registers for all devices is 0000 0000, or 0c.two additional registers store remote and local alarm threshold data corresponding to the overt output. the values stored in these registers are high-temperaturethresholds. if either of the measured temperatures equals or exceeds the corresponding alarm threshold value, an overt output asserts. the max6646/max6647 local (internal) overt register por state is 0101 0101, or +85c, while the remote (external) overt register por state is 0111 1101, or +125c. the max6649 por stateof both overt registers is 0101 0101, or +85c. diode fault alarm a continuity fault detector at dxp detects an open cir-cuit between dxp and dxn, or a dxp short to v cc , gnd, or dxn. if an open or short circuit exists, theexternal temperature register is loaded with 1111 1111. if the fault is an open-circuit fault bit 2 (open), the sta- tus byte is set to 1. in the max6649, alert is activated at the end of the conversion. immediately after por,the status register indicates that no fault is present. if a fault is present upon power-up, the fault is not indicated until the end of the first conversion. alert interrupts the alert interrupt occurs when the internal or external temperature reading exceeds a high- or low-temperaturelimit (programmed) or in the max6649, when the remote diode is disconnected (for continuity fault detection). the alert interrupt output signal is latched and can be cleared only by either reading the status register or bysuccessfully responding to an alert response address. in both cases, the alert is cleared if the fault condition no longer exists. asserting alert does not halt automatic conversion. the alert output is open drain, allowing multiple devices to share a common interrupt line. the max6646/max6647/max6649 respond to the smbus alert response address, an interrupt pointerreturn-address feature (see the alert response address section). prior to taking corrective action, always check to ensure that an interrupt is valid byreading the current temperature. fault queue register in some systems, it may be desirable to ignore a singletemperature measurement that falls outside the alert limits. bits 1 and 2 of the fault queue register (address22h) determine the number of consecutive temperature faults necessary to set alert (see tables 3 and 4). alert response address the smbus alert response interrupt pointer providesquick 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 master can broadcast a receive byte transmissionto the alert response slave address (0001 100). following such a broadcast, any slave device that gen- erated an interrupt attempts to identify itself by putting its own address on the bus. 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 conditionb = 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 masterg = msb of data clocked into master h = lsb of data clocked into master i = master pulls data line low j = acknowledge clocked into slavek = acknowledge clock pulse l = stop condition m = new start condition figure 3. smbus read timing diagram downloaded from: http:///
max6646/max6647/max6649 +145? precision smbus-compatible remote/ local sensors with overtemperature alarms 9 the alert response can activate several different slavedevices simultaneously, similar to the i 2 c general call. if more than one slave attempts to respond, bus arbitrationrules apply, and the device with the lower address code wins. the losing device does not generate an acknowl- edge 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 com-pletion of the read alert response protocol clears the interrupt latch, provided the condition that caused the alert no longer exists. overt overtemperature alarm/warning outputs overt asserts when the temperature rises to a value stored in one of the overt limit registers (19h, 20h). it deasserts when the temperature drops below the storedlimit, minus hysteresis. overt can be used to activate a cooling fan, send a warning, invoke clock throttling, or trig-ger a system shutdown to prevent component damage. command byte functions the 8-bit command byte register (table 5) is the masterindex that points to the various other registers within the max6646/max6647/max6649. the registers por state is 0000 0000, so a receive byte transmission (a protocol that lacks the command byte) that occurs immediately after por, returns the current local temperature data. the max6646/max6647/max6649 incorporate collision avoidance so that completely asynchronous operation is allowed between smbus operations and temperature conversions. one-shot the one-shot command immediately forces a new con-version cycle to begin. if the one-shot command is received while the max6646/max6647/max6649 are in standby mode ( run bit = 1), a new conversion begins, after which the device returns to standby mode. if a one-shot conversion is in progress when a one-shot com- mand is received, the command is ignored. if a one-shot command is received in autonomous mode ( run bit = 0) between conversions, a new conversion begins, the con-version rate timer is reset, and the next automatic conver- sion takes place after a full delay elapses. configuration byte functions the configuration byte register (table 6) is a read-writeregister with several functions. bit 7 is used to mask (dis- able) interrupts. bit 6 puts the max6646/max6647/ max6649 into standby mode (stop) or autonomous ( run ) mode. status byte functions the status byte register (table 7) indicates which (ifany) temperature thresholds have been exceeded. this byte also indicates whether the adc is converting and whether there is an open-circuit fault detected in the external sense junction. after por, the normal state of all flag bits is zero, assuming no alarm conditions are present. the status byte is cleared by any successful read of the status byte, after conversion is complete and if the fault condition no longer exists. note that the alert interrupt latch is not automatically cleared when the status flag bit indicating the alert is cleared. the fault condition must be eliminated before the alert output can be cleared.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 (especially when converting at the fastest rate). 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. bit name por state function 7 rfu 1 reserved. always write 1 tothis bit. 6 to 3 rfu 0 reserved. always writezero to this bit. 2 fq1 1 fault queue-length controlbit (see table 4). 1 fq0 1 fault queue-length controlbit (see table 4). 0 rfu 0 reserved. always writezero to this bit. table 3. fault queue register bit definition(22h) fq1 fq0 fault queue length (samples) 00 1 01 2 11 3 10 1 table 4. fault queue length bit definition downloaded from: http:///
max6646/max6647/max6649 +145? precision smbus-compatible remote/ local sensors with overtemperature alarms 10 conversion rate byte the conversion rate register (table 8) programs the timeinterval between conversions in free-running autonomous mode ( run = 0). this variable rate control can be used to reduce the supply current in portable-equipment appli-cations. the conversion rate bytes por state is 07h or 4hz. the max6646/max6647/max6649 look only at the 3 lsbs of this register, so the upper 5 bits are dont care bits, which should be set to zero. the conversion rate tol- erance is 25% at any rate setting. valid a/d conversion results for both channels are avail-able two total conversion times (250ms nominal, 312ms maximum) after initiating a conversion, whether conver- sion is initiated through the run bit, one-shot com- mand, or initial power-up. changing the conversion ratecan also affect the delay until new results are available. register address por state function rlts 00h 0000 0000 0c read local (internal) temperature rrte 01h 0000 0000 0c read remote (external) temperature rsl 02h n/a read status byte rcl 03h 0000 0000 read configuration byte rcra 04h 0000 0111 read conversion rate byte rlhn 05h 0101 0101 +85c read local (internal) alert high limit rlli 06h 0000 0000 0c read local (internal) alert low limit 0101 1111 +95c read remote (external) alert high limit (max6646/max6647) rrhi 07h 0101 0101 +85c read remote (external) alert high limit (max6649) rrls 08h 0000 0000 0c read remote (external) alert low limit wca 09h n/a write configuration byte wcrw 0ah n/a write conversion rate byte wlho 0bh n/a write local (internal) alert high limit wllm 0ch n/a write local (internal) alert low limit wrha 0dh n/a write remote (external) alert high limit wrln 0eh n/a write remote (external) alert low limit osht 0fh n/a one-shot reet 10h 0000 0000 0c read remote (external) extended temperature riet 11h 0000 0000 0c read local (internal) extended temperature 0111 1101 +125c read/write remote (external) overt limit (max6646/max6647) rwoe 19h 0101 0101 +85c read/write remote (external) overt limit (max6649) rwoi 20h 0101 0101 +85c read/write local (internal) overt limit hys 21h 0000 1010 10c overtemperature hysteresis queue 22h 1000 0110 fault queue feh 0100 1101 read manufacture id ffh 0101 1001 read revision id table 5. command-byte bit assignments bit name por state function 7 (msb) mask 0 masks alert interrupts when set to 1. 6 run 0 standby mode control bit; if set to 1, standby mode is initiated. 5 to 0 rfu 0 reserved. table 6. configuration-byte bit assignments (03h) downloaded from: http:///
max6646/max6647/max6649 +145? precision smbus-compatible remote/ local sensors with overtemperature alarms 11 slave addresses the max6646/max6647/max6649 have fixed slaveaddresses (see table 9). all devices also respond to the smbus alert response slave address (see the alert response address section). por and uvlo to prevent ambiguous power-supply conditions fromcorrupting the data in memory and causing erratic behavior, a por voltage detector monitors v cc and clears the memory if v cc falls below 2.0v (typ). when power is first applied and v cc rises above 2.0v (typ), the logic blocks begin operating, although reads andwrites 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 sufficientheadroom (v cc = 2.7v typ). power-up defaults power-up defaults include: ? interrupt latch is cleared. ? adc begins autoconverting at a 4hz rate. ? command byte is set to 00h to facilitate quick local temperature receive byte queries. ? local (internal) t high limit is set to +85c. ? local (internal) t low limit is set to 0c. ? remote (external) t high limit is set to +85c (max6649)/+95c (max6646/max6647) ? overt (internal) limit is set to +85c ? overt (external) limit is set to +85c (max6649)/ +125c (max6646/max6647) data conversion rate (hz) 00h 0.0625 01h 0.125 02h 0.25 03h 0.5 04h 1 05h 2 06h 4 07h 4 08h-ffh reserved table 8. conversion-rate control byte(04h) bit name por state function 7 (msb) busy 0 a/d is busy converting when 1. 6 lhigh 0 local (internal) high-temperature alarm has tripped when 1; cleared by por or readout of thestatus byte if the fault condition no longer exists. 5 llow 0 local (internal) low-temperature alarm has tripped when 1; cleared by por or readout of thestatus byte if the fault condition no longer exists. 4 rhigh 0 remote (external) high-temperature alarm has tripped when 1; cleared by por or readout of thestatus byte if the fault condition no longer exists. 3 rlow 0 remote (external) low-temperature alarm has tripped when 1; cleared by por or readout of thestatus byte if the fault condition no longer exists. 2 fault 0 a 1 indicates dxn and dxp are either shorted or open; cleared by por or readout of the statusbyte if the fault condition no longer exists. 1 eot 0 a 1 indicates the remote (external) junction temperature exceeds the external overt threshold. 0 iot 0 a 1 indicates the local (internal) junction temperature exceeds the internal overt threshold. table 7. status register bit assignments (02h) part slave address max6646 1001 101 max6647 1001 110 max6649 1001 100 table 9. slave addresses downloaded from: http:///
max6646/max6647/max6649 +145? precision smbus-compatible remote/ local sensors with overtemperature alarms 12 applications information remote-diode selection the max6646/max6647/max6649 can directly measure the die temperature of cpus and other ics that haveon-board temperature-sensing diodes (see typical operating circuit ), or they can measure the tempera- ture of a discrete diode-connected transistor. effect of ideality factor the accuracy of the remote temperature measurementsdepends on the ideality factor (n) of the remote diode (actually a transistor). the max6646/max6647/max6649 are optimized for n = 1.008, which is the typical value for the intel ? pentium ? iii and the amd athlon mp model 6. if a sense transistor with a different ideality factor is used,the output data is different. fortunately, the difference is predictable. assume a remote-diode sensor designed for a nominal ideality factor n nominal is used to measure the tem- perature of a diode with a different ideality factor n 1 . the measured temperature t m can be corrected using: where temperature is measured in kelvin.as mentioned above, the nominal ideality factor of the max6646/max6647/max6649 is 1.008. the following example uses the max6646/max6647/max6649 with a cpu that has an ideality factor of 1.002. if the diode has no series resistance, the measured data is related to the real temperature as follows: for a real temperature of +85c (358.15 k), the mea- sured temperature is +82.91c (356.02 k), which is an error of -2.13c. effect of series resistance series resistance in a sense diode contributes addition-al errors. for nominal diode currents of 10a and 100a, change in the measured voltage is: since 1c corresponds to 198.6v, series resistance contributes a temperature offset of: assume that the diode being measured has a seriesresistance of 3 . the series resistance contributes an 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 witherror due to ideality factor: 1.36c - 2.13c = -0.77c for a diode temperature of +85c.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,short the collector to the base. table 10 lists examples of discrete transistors that are appropriate for use with the max6646/max6647/max6649. avoid violating the a/d input voltage range by using a small-signal transistor with a relatively high forward volt- age. the forward voltage at the highest expected tem- perature must be greater than 0.25v at 10a, and the forward voltage at the lowest expected temperature must be less than 0.95v at 100a. do not use large power transistors. ensure that the base resistance is less than 100 . tight specifications for forward current gain (50 < ? < 150, for example) indicate that the man-ufacturer has good process controls and that the devices have consistent v be characteristics. 3 0 453 1 36 = .. c c 90 198 6 0 453 = v v c c . . vr a a ar ms s = = () 100 10 90 tt n n t actual m nominal m = ? ? ? ? ? ? = ? ? .. 1 1 008 1 002 ?? ? ? ? = t m (. ) 1 00599 tt n n m actual nominal = ? ? ? ? ? ? 1 intel and pentium are registered trademarks of intel corp. amd and athlon are trademarks of advanced micro devices, inc. manufacturer model no. central semiconductor (usa) cmpt3904 rohm semiconductor (usa) sst3904 samsung (korea) kst3904-tf siemens (germany) smbt3904 zetex (england) fmmt3904ct-nd table 10. remote-sensor transistormanufactures note: discrete transistors must be diode connected (base shorted to collector). downloaded from: http:///
adc noise filtering the integrating adc used has good noise rejection forlow-frequency signals such as 60hz/120hz power-sup- ply hum. in noisy environments, high-frequency noise reduction is needed for high-accuracy remote mea- surements. the noise can be reduced with careful pc board layout and proper external noise filtering. high-frequency emi is best filtered at dxp and dxn with an external 2200pf capacitor. larger capacitor values can be used for added filtering, but do not exceed 3300pf because larger values can introduce errors due to the rise time of the switched current source. pc board layout follow these guidelines to reduce the measurementerror of the temperature sensors: 1) place the max6646/max6647/max6649 as close as is practical to the remote diode. in noisy environ-ments, such as a computer motherboard, this dis- tance 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 isa/pci buses. 2) do not route the dxp-dxn lines next to the deflec- tion coils of a crt. also, do not route the tracesacross 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, away from any highervoltage traces, such as 12vdc. leakage currents from pc board contamination must be dealt with carefully since a 20m leakage path from dxp to ground causes about 1c error. if high-voltage tracesare unavoidable, connect guard traces to gnd on either side of the dxp-dxn traces (figure 4). 4) route through as few vias and crossunders as possi- ble to minimize copper/solder thermocouple effects. 5) when introducing a thermocouple, make sure that both the dxp and the dxn paths have matchingthermocouples. a copper-solder thermocouple exhibits 3v/c, and takes about 200v of voltage error at dxp-dxn to cause a 1c measurement error. adding a few thermocouples causes a negligi- ble error. 6) use wide traces. narrow traces are more inductive and tend to pick up radiated noise. the 10mil widthsand spacing recommended in figure 4 are not absolutely necessary, as they offer only a minor improvement in leakage and noise over narrow traces. use wider traces when practical. 7) add a 200 resistor in series with v cc for best noise filtering (see typical operating circuit ). 8) copper cannot be used as an emi shield; only fer- rous materials such as steel work well. placing acopper ground plane between the dxp-dxn traces and traces carrying high-frequency noise signals does not help reduce emi. twisted-pair and shielded cables use a twisted-pair cable to connect the remote sensorfor remote-sensor distance longer than 8in, or in very noisy environments. twisted-pair cable lengths can be between 6ft and 12ft before noise introduces excessive errors. for longer distances, the best solution is a 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 0.5c. thermal mass and self-heating when sensing local temperature, these devices areintended to measure the temperature of the pc board to which the devices are soldered. the leads provide a good thermal path between the pc board traces and the die. thermal conductivity between the die and the ambient air is poor by comparison, making air tempera- ture measurements impractical. because the thermal mass of the pc board is far greater than that of the max6646/max6647/max6649, the device follows tem- perature changes on the pc board with little or no per- ceivable delay. max6646/max6647/max6649 +145? precision smbus-compatible remote/ local sensors with overtemperature alarms 13 minimum 10 mils10 mils 10 mils 10 mils gnd dxn dxp gnd figure 4. recommended dxp-dxn pc traces downloaded from: http:///
mux remote local adc 2 control logic smbus read write 8 8 addressdecoder 7 s r q diode fault dxp dxn sclk sda register bank command byte remote temperature local temperature alert threshold alert response address v cc s r q overt gnd alert max6646/max6647/max6649 overt threshold functional diagram max6646/max6647/max6649 when measuring the temperature of a cpu or other icwith 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 sen- sors, smaller packages, such as sc70s or sot23s, yield the best thermal response times. 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 mea- surement accuracy. self-heating does not significantly affect measurementaccuracy. remote-sensor self-heating due to the diode current source is negligible. for the local diode, the worst-case error occurs when autoconverting at the fastest rate and simultaneously sinking maximum cur- rent at the alert output. for example, with v cc = 5.0v, at a 4hz conversion rate and with alert sinking 1ma, the typical power dissipation is: 5.0v x 500a + 0.4v x 1ma = 2.9mw ? j-a for the 8-pin max package is +221c/w, so assuming no copper pc board heat sinking, the result-ing temperature rise is: ? t = 2.9mw x +221c/w = +0.6409c even under nearly worst-case conditions, it is difficult tointroduce a significant self-heating error. +145? precision smbus-compatible remote/ local sensors with overtemperature alarms 14 downloaded from: http:///
max6646/max6647/max6649 +145? precision smbus-compatible remote/ local sensors with overtemperature alarms 12 34 8 7 6 5 sclk sda gnd dxn dxp v cc max6646 max6647 max6649 max + top view overt alert pin configuration chip information process: bicmos 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 pertains to the package regardless of rohs status. por values part address external oert limit (c) external alert t high limit (c) alert asserted while diode open max6646 1001 101 +125 +95 no max6647 1001 110 +125 +95 no max6649 1001 100 +85 +85 yes selector guide 15 package type package code outline no. land pattern no. 8 max u8+1 21-0036 90-0092 downloaded from: http:///
max6646/max6647/max6649 +145? precision smbus-compatible remote/ local sensors with overtemperature alarms maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circuit patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. the parametric values (min and max limits) shown in the electrical characteristics table are guaranteed. other parametric values quoted in this data sheet are provided for guidance. 16 _______________maxim integrated products, inc. 160 rio robles, san jose, ca 95134 usa 1-408-601-1000 ? 2012 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. revision history revision number revision date description pages changed 4 7/12 updated the ordering information table to include lead-free packages; added the soldering temperature value to the absolute maimum ratings section; added the package information table; updated the electrical characteristics table for the following: 1) removed the start condition setup time parameter 2) changed t su:sta(min) from 50ns to 4.7ns and removed the 90% to 90% condition 3) updated the data setup time parameter symbol and added the data hold time parameter 1, 2, 3, 15 downloaded from: http:///

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