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1c accurate 8-channel temperature sensor max6581 evaluation kit available 19-5260; rev 1; 2/13 ordering information/selector guide general description the max6581 precision multichannel temperature sensor monitors its own temperature and the tempera - tures of up to seven external diode-connected transis - tors. all temperature channels have programmable alert and overtemperature thresholds. when the measured temperature of a channel crosses the respective thresh - old, a status bit is set in one of the status registers. two open-drain alarm outputs ( alert and overt ) assert corresponding to these bits in the status register(s).resistance cancellation is available for all channels and compensates for high series resistance in circuit-board traces and thermal diodes. the 2-wire serial interface accepts smbus protocols (write byte, read byte, send byte, and receive byte) for reading the temperature data and programming the alarm thresholds. the max6581 is specified for an operating temperature range of -40 n c to +125 n c and is available in a 24-pin, 4mm x 4mm thin qfn package with an exposed pad. features s eight channels to measure seven remote and one local temperature s 11-bit, 0.125 n c resolution s high accuracy of 1 n c (max) from +60 n c to +100 n c (remote channels) s -64 n c to +150 n c remote temperature range s programmable undertemperature/overtemperature alerts s smbus/i 2 c-compatible interface s two open-drain alarm outputs ( alert and overt ) s resistance cancellation on all remote channels applications desktop computersnotebook computers workstations servers data communications note: all devices are specified over the -40 n c to +125 n c operating temperature range. + denotes a lead(pb)-free/rohs-compliant package. * ep = exposed pad. ** future product?contact factory for availability. typical application circuit appears at end of data sheet. part slave address pin-package operating temperature range measured temperature range max6581tg9a+ 0x9a 24 tqfn-ep* -40 n c to +125 n c -64 n c to +150 n c max6581tg9c+** 0x9c 24 tqfn-ep* -40 n c to +125 n c -64 n c to +150 n c max6581tg9e+** 0x9e 24 tqfn-ep* -40 n c to +125 n c -64 n c to +150 n c max6581tg98+** 0x98 24 tqfn-ep* -40 n c to +125 n c -64 n c to +150 n c for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim integrated?s website at www.maximintegrated.com. downloaded from: http:///
2 maxim integrated 1c accurate 8-channel temperature sensor max6581 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 gnd.)v cc , smbclk, smbdata, alert , overt , stby to gnd ......................................... -0.3v to +4v dxp_ to gnd ............................................ -0.3v to (v cc + 0.3v) dxn_ to gnd ........................................... -0.3v to (v cc + 0.3v) smbdata, alert , overt current .................. -1ma to +50ma dxn_ current .................................................................... q 1ma continuous power dissipation (t a = +70 n c) tqfn (derate 27.8mw/ n c above +70 n c) ................... 2222mw esd protection (all pins, human body model) ................... q 2kv operating temperature range ........................ -40 n c to +125 n c junction temperature ..................................................... +150 n c storage temperature range .......................... -65 n c to +150 n c lead temperature (soldering, 10s) ............................... +300 n c soldering temperature (reflow) ...................................... +260 n c electrical characteristics (v cc = +3.0v to +3.6v, t a = -40 n c to +125 n c, unless otherwise noted. typical values are at v cc = +3.3v and t a = +25 n c.) (note 2) absolute maximum ratings note 1: package thermal resistances were obtained using the method described in jedec specification jesd51-7, using a four-layer board. for detailed information on package thermal considerations, refer to www.maximintegrated.com/thermal-tutorial . package thermal characteristics (note 1) tqfn junction-to-ambient thermal resistance ( b ja ) ...... 36.0 n c/w junction-to-case thermal resistance ( b jc ) .............. 3.0 n c/w parameter symbol conditions min typ max units supply voltage v cc 3.0 3.6 v standby supply current i ss smbus static 4 15 f a operating current i cc1 during conversion, rc off 500 600 f a i cc2 during conversion, rc on 550 650 temperature resolution 11 bits 0.125 n c 3-sigma temperature accuracy (remote channels 1?7) v cc = 3.3v t a = +30 n c to +85 n c, t rj = +60 n c to +100 n c -0.85 +0.85 n c t a , t rj = -40 n c to +125 n c -1.2 +1.2 t a = +30 n c to +85 n c, t rj = +100 n c to +150 n c -2.5 +2.5 3-sigma temperature accuracy (local) v cc = 3.3v t a = +30 n c to +85 n c -1 +1 n c t a = -40 n c to +125 n c -2 +2 t a = 0 n c to +150 n c -3 +3 6-sigma temperature accuracy (remote channels 1?7) v cc = 3.3v t a = +30 n c to +85 n c, t rj = +60 n c to +100 n c -1 +1 n c t a , t rj = -40 n c to +125 n c -2 +2 t a = +30 n c to +85 n c, t rj = +100 n c to +125 n c -2.75 +2.75 6-sigma temperature accuracy (local) v cc = 3.3v t a = +30 n c to +85 n c -1.5 +1.5 n c t a = -40 n c to +125 n c -2.5 +2.5 t a = 0 n c to +150 n c -3.5 +3.5 downloaded from: http:///
3 maxim integrated 1c accurate 8-channel temperature sensor max6581 electrical characteristics (continued) (v cc = +3.0v to +3.6v, t a = -40 n c to +125 n c, unless otherwise noted. typical values are at v cc = +3.3v and t a = +25 n c.) (note 2) parameter symbol conditions min typ max units supply sensitivity of temperature accuracy q 0.2 n c/v conversion time per channel t conv resistance cancellation mode off 95 125 156 ms resistance cancellation mode on or beta compensation on 190 250 312 remote-diode source current i rj high level resistance cancellation mode off 80 100 120 f a low level 8 10 12 high level resistance cancellation mode on or beta compensation on 160 200 240 low level 16 20 24 dxp_ and dxn_ leakage current standby mode 100 na undervoltage lockout threshold uvlo falling edge of v cc disables adc 2.25 2.80 2.95 v undervoltage lockout hysteresis 90 mv power-on-reset (por) threshold v cc falling edge 1.3 2.0 2.2 v por threshold hysteresis 90 mv alert and overt output low voltage v ol i sink = 1ma 0.01 v i sink = 6ma 0.3 input leakage current i leak -1 +1 f a smbus interface, stby logic input low voltage v il v cc = 3.6v 0.8 v logic input high voltage v ih v cc = 3.0v 2.2 v input leakage current -1 +1 f a output low voltage v ol i sink = 6ma 0.1 v input capacitance c in 5 pf smbus-compatible timing (figures 3 and 4) (note 3)serial-clock frequency f smbclk (note 4) 400 khz bus free time between stop and start condition t buf f smbclk = 400khz 1.6 f s start condition setup time f smbclk = 400khz 0.6 f s repeated start condition setup time t su:sta 90% of smbclk to 90% of smbdata, f smbclk = 400khz 50 ns start condition hold time t hd:sta 10% of smbdata to 90% of smbclk, f smbclk = 400khz 0.6 f s stop condition setup time t su:sto 90% of smbclk to 90% of smbdata, f smbclk = 400khz 0.6 f s clock low period t low 10% to 10%, f smbclk = 400khz 1 f s clock high period t high 90% to 90% 0.6 f s data-in hold time t hd:dat 0 0.9 us data-in setup time t su:dat (note 5) 100 ns downloaded from: http:///
4 maxim integrated 1c accurate 8-channel temperature sensor max6581 typical operating characteristics (v cc = +3.3v, v stby = v cc , t a = +25 n c, unless otherwise noted.) electrical characteristics (continued) (v cc = +3.0v to +3.6v, t a = -40 n c to +125 n c, unless otherwise noted. typical values are at v cc = +3.3v and t a = +25 n c.) (note 2) note 2: all parameters are tested at t a = +85 n c. specifications over temperature are guaranteed by design. note 3: timing specifications are guaranteed by design. note 4: the serial interface resets when smbclk is low for more than t timeout . note 5: a transition must internally provide at least a hold time to bridge the undefined region (300ns max) of smbclk?s falling edge. standby supply current vs. supply voltage max6581 toc01 supply voltage (v) standby supply current (a) 3.5 3.4 3.3 3.2 3.1 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 0 3.0 3.6 hardware or softwarestandby supply current average operating supply current vs. supply voltage max6581 toc02 supply voltage (v) average operating supply current (a) 3.5 3.4 3.1 3.2 3.3 365 370 375 380 385 390 395 400360 3.0 3.6 resistancecancellation off remote-diode temperature error vs. remode-diode temperature max6581 toc03 remote-diode temperature (c) remote-diode temperature error (c) 110 90 50 70 30 10 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 -4-5 -6 -7 -8 -9 -10 -10 130 parameter symbol conditions min typ max units receive smbclk/smbdata rise time t r 300 ns receive smbclk/smbdata fall time t f 300 ns data-out hold time t dh 50 ns pulse width of spike suppressed t sp 0 50 ns smbus timeout t timeout smbdata low period for interface reset 25 37 45 ms downloaded from: http:///
5 maxim integrated 1c accurate 8-channel temperature sensor max6581 typical operating characteristics (continued)(v cc = +3.3v, v stby = v cc , t a = +25 n c, unless otherwise noted.) local temperature error vs. die temperature max6581 toc04 die temperature (c) local temperature error (c) 90 80 60 70 10 20 30 40 50 0 -4 -3 -2 -1 0 1 2 3 4 5 -5 -10 100 remote-diode temperature error vs. power-supply noise frequency max6581 toc05 power-supply noise frequency (mhz) remote-diode temperature error (c) 1 0.1 0.01 -4 -3 -2 -1 0 1 2 3 4 5 -5 0.001 10 100mv p-p t rj = +85c local temperature error vs. power-supply noise frequency max6581 toc06 power-supply noise frequency (mhz) local temperature error (c) 1 0.1 0.01 -4 -3 -2 -1 0 1 2 3 4 5 -5 0.001 10 100mv p-p remote-diode temperature error vs. capacitance max6581 toc07 capacitance (nf) remote-diode temperature error (c) 10 -4 -3 -2 -1 0 1 2 3 4 5 -5 1 100 100mv p-p t rj = +85c remote-diode temperature error vs. resistance max6581 toc08 resistance ( i ) remote-diode temperature error (c) 90 80 60 70 20 30 40 50 10 0 5 10 15 20 25 30 35 40 45 50 -5 0 100 t rj = +85c resistancecancellation off resistancecancellation on downloaded from: http:///
6 maxim integrated 1c accurate 8-channel temperature sensor max6581 pin configuration pin description pin name function 1 dxp2 combined current source and adc positive input for channel 2 remote diode. connect dxp2 to the anode of a remote-diode-connected, temperature-sensing transistor. leave dxp2 unconnected or connect to dxn2 if a remote diode is not used. connect a 100pf capacitor between dxp2 and dxn2 for noise filtering. 2 dxn2 cathode input for channel 2 remote diode. connect the cathode of the channel 2 remote-diode-connected transistor to dxn2. if the channel 2 remote transistor is a substrate pnp (e.g., on a cpu die), connect the base of the pnp to dxn2. leave dxn2 unconnected or connect to dxp2 if a remote diode is not used. connect a 100pf capacitor between dxp2 and dxn2 for noise filtering. 3 dxp3 combined current source and adc positive input for channel 3 remote diode. connect dxp3 to the anode of a remote-diode-connected, temperature-sensing transistor. leave dxp3 unconnected or connect to dxn3 if a remote diode is not used. connect a 100pf capacitor between dxp3 and dxn3 for noise filtering. 4 dxn3 cathode input for channel 3 remote diode. connect the cathode of the channel 3 remote-diode-connected transistor to dxn3. if the channel 3 remote transistor is a substrate pnp (e.g., on a cpu die), connect the base of the pnp to dxn3. leave dxn3 unconnected or connect to dxp3 if a remote diode is not used. connect a 100pf capacitor between dxp3 and dxn3 for noise filtering. 5 dxp4 combined current source and adc positive input for channel 4 remote diode. connect dxp4 to the anode of a remote-diode-connected, temperature-sensing transistor. leave dxp4 unconnected or connect to dxn4 if a remote diode is not used. connect a 100pf capacitor between dxp4 and dxn4 for noise filtering. 6, 22 n.c. no connection. connect to other n.c. or leave unconnected. 2324 22 21 87 9 dxn2dxn3 dxp4 n.c. 10 dxp2 v cc i.c.stby alertdxp7 12 n.c. 45 6 17 18 16 14 13 dxp1 dxn1 dxn6dxn5 dxp5 dxn4 max6581 dxp3 overt 3 15 gnd 20 11 dxp6 smbclk 19 12 dxn7 smbdata top view *ep = exposed pad, connect to gnd *ep downloaded from: http:///
7 maxim integrated 1c accurate 8-channel temperature sensor max6581 pin description (continued) pin name function 7 dxn4 cathode input for channel 4 remote diode. connect the cathode of the channel 4 remote-diode-connected transistor to dxn4. if the channel 4 remote transistor is a substrate pnp (e.g., on a cpu die), connect the base of the pnp to dxn4. leave dxn4 unconnected or connect to dxp4 if a remote diode is not used. connect a 100pf capacitor between dxp4 and dxn4 for noise filtering. 8 dxp5 combined current source and adc positive input for channel 5 remote diode. connect dxp5 to the anode of a remote-diode-connected, temperature-sensing transistor. leave dxp5 unconnected or connect to dxn5 if a remote diode is not used. connect a 100pf capacitor between dxp5 and dxn5 for noise filtering. 9 dxn5 cathode input for channel 5 remote diode. connect the cathode of the channel 5 remote-diode-connected transistor to dxn5. if the channel 5 remote transistor is a substrate pnp (e.g., on a cpu die), connect the base of the pnp to dxn5. leave dxn5 unconnected or connect to dxp5 if a remote diode is not used. connect a 100pf capacitor between dxp5 and dxn5 for noise filtering. 10 dxn6 cathode input for channel 6 remote diode. connect the cathode of the channel 6 remote-diode-connected transistor to dxn6. if the channel 6 remote transistor is a substrate pnp (e.g., on a cpu die), connect the base of the pnp to dxn6. leave dxn6 unconnected or connect to dxp6 if a remote diode is not used. connect a 100pf capacitor between dxp6 and dxn6 for noise filtering. 11 dxp6 combined current source and adc positive input for channel 6 remote diode. connect dxp6 to the anode of a remote-diode-connected, temperature-sensing transistor. leave dxp6 unconnected or connect to dxn6 if a remote diode is not used. connect a 100pf capacitor between dxp6 and dxn6 for noise filtering. 12 dxn7 cathode input for channel 7 remote diode. connect the cathode of the channel 7 remote-diode-connected transistor to dxn7. if the channel 7 remote transistor is a substrate pnp (e.g., on a cpu die), connect the base of the pnp to dxn7. leave dxn7 unconnected or connect to dxp7 if a remote diode is not used. connect a 100pf capacitor between dxp7 and dxn7 for noise filtering. 13 dxp7 combined current source and adc positive input for channel 7 remote diode. connect dxp7 to the anode of a remote-diode-connected, temperature-sensing transistor. leave dxp7 unconnected or connect to dxn7 if a remote diode is not used. place a 100pf capacitor between dxp7 and dxn7 for noise filtering. 14 stby active-low standby input. drive stby logic-low to place the max6581 in standby mode, or logic- high for normal mode. temperature and threshold data are retained in standby mode. 15 i.c. internally connected. i.c. is internally connected to v cc . connect i.c. to v cc or leave unconnected. 16 overt overtemperature active-low, open-drain output. overt asserts low when the temperature of any remote channel exceeds the programmed threshold limit. 17 v cc supply voltage input. bypass to gnd with a 0.1 f f capacitor. 18 alert smbus alert (interrupt), active-low, open-drain output. alert asserts low when the temperature of any channel crosses a programmed alert high or low threshold. 19 smbdata smbus serial-data input/output. connect smbdata to a pullup resistor. 20 smbclk smbus serial-clock input. connect smbclk to a pullup resistor. downloaded from: http:///
8 maxim integrated 1c accurate 8-channel temperature sensor max6581 detailed description the max6581 is a precision multichannel temperature monitor that features one local and seven remote tem - perature-sensing channels with a programmable alert threshold for each temperature channel and a program - mable overtemperature threshold for channels 1?7 (see figure 1). communication with the max6581 is achieved through the smbus serial interface and a dedicated alert pin ( alert ). the alarm outputs, ( overt and alert ) assert if the software-programmed temperature thresh - olds are exceeded. alert also asserts if the measured temperature falls below the alert low limits. alert typically serves as an interrupt, while overt can be connected to a fan, system shutdown, or other thermal-management circuitry. adc conversion sequence the max6581 starts the conversion sequence by measuring the temperature on channel 1, followed by 2, local channel, 3?7. the conversion result for each active channel is stored in the corresponding temperature data register. no conversion is performed on any channel that does not have a diode. low-power standby mode enter software-standby mode by setting the stop bit to 1 in the configuration register. enter hardware- standby by pulling stby low. software-standby mode disables the adc and reduces the supply current to approximately 4 f a. during either software or hardware standby, data is retained in memory. during hardware standby, the smbus interface is inactive. during software standby, the smbus interface is active and listening for commands. the timeout is enabled if a start condition is recognized on smbus. activity on the smbus causes the supply current to increase. if a standby command is received while a conversion is in progress, the conver - sion cycle is interrupted, and the temperature registers are not updated. the previous data is not changed and remains available. operating-current calculation the max6581 operates at different operating-current levels depending on how many external channels are in use and how many of those are in resistance cancella - tion (rc) mode. the average operating current is: nr av cc1 cc2 nr nr n 1 2n ii i n 2n 1 n 2n 1 + = + + + + + where:n n = the number of remote channels that are operating in normal mode.n r = the number of remote channels that are in rc mode.i av = the average operating power-supply current over a complete series of conversions.i cc1 = the average operating power-supply current during a conversion in normal mode.i cc2 = the average operating power-supply current during a conversion in rc mode. pin description (continued) pin name function 21 gnd ground 23 dxp1 combined current source and adc positive input for channel 1 remote diode. connect dxp1 to the anode of a remote-diode-connected, temperature-sensing transistor. leave dxp1 unconnected or connect to dxn1 if a remote diode is not used. connect a 100pf capacitor between dxp1 and dxn1 for noise filtering. 24 dxn1 cathode input for channel 1 remote diode. connect the cathode of the channel 1 remote-diode-connected transistor to dxn1. if the channel 1 remote transistor is a substrate pnp (e.g., on a cpu die), connect the base of the pnp to dxn1. leave dxn1 unconnected or connect to dxp1 if a remote diode is not used. connect a 100pf capacitor between dxp1 and dxn1 for noise filtering. ? ep exposed pad. connect ep to gnd. downloaded from: http:///
9 maxim integrated 1c accurate 8-channel temperature sensor max6581 figure 1. internal block diagram v cc dxn2 dxp2 dxn1 dxp1 dxn3 dxp3 dxn4 dxp4 dxn5 dxp5 dxn6 dxp6 localtransistor smbclk smbdata input buffer ref counter smbus interface count +- dxn7 dxp7 i rj register bank command byte remote temperatures local temperatures stby overt alert threshold overt threshold alert response address alert alarm alu max6581 downloaded from: http:///
10 maxim integrated 1c accurate 8-channel temperature sensor max6581 smbus digital interface from a software perspective, the max6581 appears as a series of 8-bit registers that contain temperature- measurement data, alarm threshold values, and control bits. a standard smbus-compatible, 2-wire serial inter - face is used to read temperature data and write control bits and alarm threshold data. the same smbus slave address also provides access to all functions. the max6581 employs four standard smbus proto - cols: write byte, read byte, send byte, and receive byte (figure 2). the shorter receive-byte protocol allows quicker transfers, provided that the correct data regis - ter was previously selected by a read-byte instruction. use caution with the shorter protocols in multimaster systems, since a second master could overwrite the command byte without informing the first master. figure 3 is the smbus write timing diagram and figure 4 is the smbus read timing diagram. the remote-diode-measurement channels provide 11 bits of data (1 lsb = 0.125 n c). the eight most significant bits (msbs) can be read from the local tem - perature and remote temperature registers. the remain - ing 3 bits for remote can be read from the extended temperature register. if extended resolution is desired, the extended-resolution register should be read first. this prevents the msbs from being overwritten by new conversion results until they have been read. if the msbs have not been read within a smbus timeout period (nom - inally 37ms), normal updating continues. table 1 shows the main temperature register (high-byte) data format and table 2 shows the extended-resolution register (low- byte) data format. figure 2. smbus protocols s address wr ack ack p data ack command 7 bits 1 8 bits 8 bits slave address: equivalentto chip-select line of a 3-wire interface data byte: data goes into the registerset by the command byte (to set thresholds, configuration masks, and sampling rate) write-byte format s address address wr ack ack p s rd ack /// data command 7 bits 7 bits 8 bits 8 bits read-byte format slave address: equivalentto chip select line command byte: selectswhich register you are reading from sp address wr ack ack command 7 bits 8 bits send-byte format command byte: sends commandwith no data, usually used for one-shot command sp address rd ack /// data 7 bits 8 bits receive-byte format data byte: reads data fromthe register commanded by the last read-byte or write-byte transmission; also used for smbus alert response return address slave address: repeateddue to change in data- flow direction data byte: reads fromthe register set by the command byte s = start conditionp = stop condition shaded = slave transmission/// = not acknowledged downloaded from: http:///
11 maxim integrated 1c accurate 8-channel temperature sensor max6581 figure 3. smbus write timing diagramfigure 4. read-timing diagram 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 = slave pulls data line lowj = acknowledge clocked into master k = acknowledge clock pulse l = stop condition m = new start condition smbclk ab cd e fg h i 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 j k f = acknowledge bit clocked into masterg = msb of data clocked into master h = lsb of data clocked into master i = acknowledge clock pulsej = stop condition k = new start condition downloaded from: http:///
12 maxim integrated 1c accurate 8-channel temperature sensor max6581 table 2. extended-resolution temperature register (low-byte) data format x = don?t care. table 1. main temperature register (high-byte) data format temperature ( n c) digital output 0 000x xxxx +0.125 001x xxxx +0.250 010x xxxx +0.375 011x xxxx +0.500 100x xxxx +0.625 101x xxxx +0.750 110x xxxx +0.875 111x xxxx temperature ( n c) digital output normal format extrange = 0 extended format extrange = 1 diode fault (open or short) 1111 1111 1111 1111 > +254 1111 1111 1111 1111 +254 1111 1110 1111 1111 +191 1101 1111 1111 1111 +190 1101 1110 1111 1110 +125 0111 1101 1011 1101 +85 0101 0101 1001 0101 +25 0001 1001 0101 1001 0 0000 0000 0100 0000 -1 0000 0000 0011 1111 -40 0000 0000 0001 1000 -63 0000 0000 0000 0001 -64 0000 0000 0000 0000 < -64 0000 0000 0000 0000 downloaded from: http:///
13 maxim integrated 1c accurate 8-channel temperature sensor max6581 table 3. command byte register bit assignment register address (hex) por value (hex) read/ write description remote 1 01 00 r read channel 1 remote temperature remote 2 02 00 r read channel 2 remote temperature remote 3 03 00 r read channel 3 remote temperature remote 4 04 00 r read channel 4 remote temperature remote 5 05 00 r read channel 5 remote temperature remote 6 06 00 r read channel 6 remote temperature local 07 00 r read local temperature remote 7 08 00 r read channel 7 remote temperature remote 1 extended bits* 09 00 r read channel 1 remote-diode extended temperature manufacturer id 0a 4d r read manufacturer id revision id 0f 00 r read revision id remote 1 alert high limit 11 7f r/w read/write channel 1 remote-diode alert high-temperature threshold limit remote 2 alert high limit 12 7f r/w read/write channel 2 remote-diode alert high-temperature threshold limit remote 3 alert high limit 13 64 r/w read/write channel 3 remote-diode alert high-temperature threshold limit remote 4 alert high limit 14 64 r/w read/write channel 4 remote-diode alert high-temperature threshold limit remote 5 alert high limit 15 64 r/w read/write channel 5 remote-diode alert high-temperature threshold limit remote 6 alert high limit 16 64 r/w read/write channel 6 remote-diode alert high-temperature threshold limit local alert high limit 17 5a r/w read/write local-diode alert high-temperature threshold limit remote 7 alert high limit 18 64 r/w read/write channel 7 remote-diode alert high-temperature threshold limit local overt high limit 20 50 r/w read/write channel local-diode overtemperature threshold limit remote 1 overt high limit 21 6e r/w read/write channel 1 remote-diode overtemperature threshold limit remote 2 overt high limit 22 6e r/w read/write channel 2 remote-diode overtemperature threshold limit remote 3 overt high limit 23 6e r/w read/write channel 3 remote-diode overtemperature threshold limit remote 4 overt high limit 24 7f r/w read/write channel 4 remote-diode overtemperature threshold limit remote 5 overt high limit 25 5a r/w read/write channel 5 remote-diode overtemperature threshold limit remote 6 overt high limit 26 5a r/w read/write channel 6 remote-diode overtemperature threshold limit downloaded from: http:///
14 maxim integrated 1c accurate 8-channel temperature sensor max6581 table 3. command byte register bit assignment (continued) * duplicate entries. register address (hex) por value (hex) read/ write description remote 7 overt high limit 27 5a r/w read/write channel 7 remote-diode overtemperature threshold limit alert low limits (all channels) 30 00 r/w read/write all channels alert low-temperature threshold limit configuration 41 00 r/w read/write configuration alert mask 42 00 r/w read/write alert mask overt mask 43 00 r/w read/write overt mask alert high status 44 00 r read alert high status overt status 45 00 r read overt status diode fault status 46 00 r read diode fault status alert low status 47 00 r read alert low status alert low disable 48 ff r/w read/write alert low disable resistance cancellation 4a 00 r/w read/write resistance cancellation enable bits (1 = on, 0 = off) transistor ideality 4b 00 r/w read/write ideality value for remote-sense transistor ideality select 4c 00 r/w read/write ideality value selection bits (1 = selected transistor ideality, 0 = 1.008) offset 4d 00 r/w read/write temperature offset value offset select 4e 00 r/w read/write offset value selection bits (1 = value in offset register, 0 = 0) remote 1 extended bits* 51 00 r read channel 1 remote extended temperature remote 2 extended bits 52 00 r read channel 2 remote extended temperature remote 3 extended bits 53 00 r read channel 3 remote extended temperature remote 4 extended bits 54 00 r read channel 4 remote extended temperature remote 5 extended bits 55 00 r read channel 5 remote extended temperature remote 6 extended bits 56 00 r read channel 6 remote extended temperature local extended bits 57 00 r read local channel extended temperature remote 7 extended bits 58 00 r read channel 7 remote extended temperature downloaded from: http:///
15 maxim integrated 1c accurate 8-channel temperature sensor max6581 diode fault detection if a channel?s input dxp_ and dxn_ are left open or are shorted, the max6581 detects a diode fault. an open diode fault does not cause either alert or overt to assert. a bit in the status register for the correspond - ing channel is set to 1 and the temperature data for the channel is stored as all 1s (ffh). it takes approximately 4ms for the max6581 to detect a diode fault. once a diode fault is detected, the max6581 goes to the next channel in the conversion sequence. alarm threshold registers there are 17 alarm threshold registers that store over - temperature and undertemperature alert and overt threshold values. nine of these registers are dedicated to storing one local alert overtemperature threshold limit, seven remote alert overtemperature threshold limits, and one shared alert undertemperature temperature thresh - old limit (see the alert interrupt mode section). the remaining eight registers are dedicated to storing one local overtemperature threshold limit and seven remote channels to store overtemperature threshold limits (see the overt overtemperature alarms section). access to these registers is provided through the smbus interface. alert interrupt mode alert interrupts occur when the internal or external temperature reading exceeds a high-temperature limit (user programmable) or a low-temperature limit. the alert interrupt output signal can be cleared by reading the status register(s) associated with the fault(s) or by successfully responding to an alert response address transmission by the master. in both cases, the alert is cleared but is reasserted at the end of the next conver - sion if the fault condition still exists. the interrupt does not halt automatic conversions. the alert output is open-drain so that multiple devices can share a common interrupt line. all alert interrupts can be masked using the alert mask register (42h). the por state of these registers is shown in table 3. alert responses address the smbus alert response interrupt pointer provides quick fault identification for simple slave devices that lack the complex logic necessary to be a bus master. upon receiving an interrupt signal, the host master can broadcast a receive-byte transmission to the alert response slave address (19h). then, any slave device that generated an interrupt attempts to identify itself by putting its own address on the bus. the alert response can activate several different slave devices simultaneously, similar to the i 2 c general call. if more than one slave attempts to respond, bus arbitra - tion rules apply, and the device with the lower address code wins. the losing device does not generate an acknowledgment and continues to hold the alert line low until cleared (the conditions for clearing an alert vary depending on the type of slave device.) successful completion of the alert response protocol clears the out - put latch. if the condition that caused the alert still exists, the max6581 reasserts the alert interrupt at the end of the next conversion. overt overtemperature alarms the max6581 has eight overtemperature registers that store alarm threshold data for the overt output. overt is asserted when a channel?s measured temperature is greater than the value stored in the corresponding threshold register. overt remains asserted until the temperature drops below the programmed threshold minus 4 n c hysteresis. an overtemperature output can be used to activate a cooling fan, send a warning, initiate clock throttling, or trigger a system shutdown to prevent component damage. see table 3 for the por state of the overtemperature threshold registers. command byte register functions the 8-bit command byte register (table 3) is the master index that points to the various other registers within the max6581. this register?s por state is 0000 0000 (00h). configuration register (41h) the configuration register (table 4) has several functions. bit 7 (msb) is used to put the max6581 either in software-standby mode (stop) or continuous- conversion mode. bit 6 resets all registers to their por conditions and then clears itself. bit 5 disables the smbus timeout. bit 1 sets the extended range of the remote temperature diodes. the remaining bits of the configuration register are not used. the por state of this register is 0000 0000 (00h). alert mask register (42h) the alert mask register functions are described in table 5. bits [7:0] are used to mask the alert interrupt output. bit 6 masks the local alert interrupt and the remaining bits mask the remote alert interrupts. the power-up state of this register is 0000 0000 (00h). overt mask register (43h) table 6 describes the overt mask register. bit 6 and the remaining bits mask the overt interrupt output for all channels. the power-up state of this register is 0000 0000 (00h). downloaded from: http:///
16 maxim integrated 1c accurate 8-channel temperature sensor max6581 table 4. configuration register (41h)table 5. alert mask register (42h) table 6. overt mask register (43h) bit name por value function 7 (msb) stop 0 standby-mode control bit. if stop is set to logic 1, the max6581 stops converting and enters standby mode. 6 por 0 reset bit. set to logic 1 to put the device into its power-on state. this bit is self-clearing. 5 timeout 0 timeout enable bit. set to logic 0 to enable smbus timeout. 4 reserved 0 reserved. must be set to 0. 3 reserved 0 reserved. must be set to 0. 2 reserved 0 reserved. must be set to 0. 1 extrange 0 extended-range enable bit. set bit 1 to logic 1 to set the temperature and limit data range to -64 n c to +191 n c. set bit 1 to logic 0 to set the range to 0 n c to +255 n c. 0 reserved 0 reserved. must be set to 0. bit name por value function 7 (msb) mask alert 7 0 channel 7 alert mask. set to logic 1 to mask channel 7 alert . 6 mask local alert 0 local alert mask. set to logic 1 to mask local channel alert . 5 mask alert 6 0 channel 6 alert mask. set to logic 1 to mask channel 6 alert . 4 mask alert 5 0 channel 5 alert mask. set to logic 1 to mask channel 5 alert . 3 mask alert 4 0 channel 4 alert mask. set to logic 1 to mask channel 4 alert . 2 mask alert 3 0 channel 3 alert mask. set to logic 1 to mask channel 3 alert . 1 mask alert 2 0 channel 2 alert mask. set to logic 1 to mask channel 2 alert . 0 mask alert 1 0 channel 1 alert mask. set to logic 1 to mask channel 1 alert . bit name por value function 7 (msb) mask overt 7 0 channel 7 remote-diode overt mask bit. set to logic 1 to mask channel 7 overt . 6 mask local overt 0 local overt mask. set to logic 1 to mask local channel overt . 5 mask overt 6 0 channel 6 remote-diode overt mask bit. set to logic 1 to mask channel 6 overt . 4 mask overt 5 0 channel 5 remote-diode overt mask bit. set to logic 1 to mask channel 5 overt . 3 mask overt 4 0 channel 4 remote-diode overt mask bit. set to logic 1 to mask channel 4 overt . 2 mask overt 3 0 channel 3 remote-diode overt mask bit. set to logic 1 to mask channel 3 overt . 1 mask overt 2 0 channel 2 remote-diode overt mask bit. set to logic 1 to mask channel 2 overt . 0 mask overt 1 0 channel 1 remote-diode overt mask bit. set to logic 1 to mask channel 1 overt . downloaded from: http:///
17 maxim integrated 1c accurate 8-channel temperature sensor max6581 status register functions there are four status registers (see tables 7?10). the alert high status register indicates whether a mea - sured local or remote temperature has exceeded the associated threshold limit set in an alert high limit register. the overt status register indicates whether a measured temperature has exceeded the associated threshold limit set in an overt high limit register. the diode fault status register indicates whether there is a diode fault (open or short) in any of the remote-sensing channels. the alert low status register indicates whether the measured temperature has fallen below the threshold limit set in the alert low limits register for the local or remote-sensing diodes.bits in the alert status registers are cleared by a success - ful read, but set again after the next conversion unless the fault is corrected, either by a drop in the measured temperature or a change in the threshold temperature. the alert interrupt output follows the status flag bit. once the alert output is asserted, it can be deasserted by either reading the alert high status register or by successfully responding to an alert response address. in both cases, the alert is cleared even if the fault condition exists, but the alert output reasserts at the end of the next conversion.the bits indicating overt faults clear only when the measured temperature drops below the temperature threshold minus the hysteresis value (4 n c), or when the trip temperature is set to a value at least 4 n c above the current temperature. table 7. alert high status register (44h) bit name por state function 7 (msb) remote alert high 7 0 channel 7 remote-diode high-alert bit. this bit is set to logic 1 when the channel 7 remote-diode temperature exceeds the programmed temperature threshold limit in the remote 7 alert high limit register. 6 local alert high 0 local channel high-alert bit. this bit is set to logic 1 when the local temperature exceeds the temperature threshold limit in the local alert high limit register. 5 remote alert high 6 0 channel 6 remote-diode high-alert bit. this bit is set to logic 1 when the channel 6 remote-diode temperature exceeds the programmed temperature threshold limit in the remote 6 alert high limit register. 4 remote alert high 5 0 channel 5 remote-diode high-alert bit. this bit is set to logic 1 when the channel 5 remote-diode temperature exceeds the programmed temperature threshold limit in the remote 5 alert high limit register. 3 remote alert high 4 0 channel 4 remote-diode high-alert bit. this bit is set to logic 1 when the channel 4 remote-diode temperature exceeds the programmed temperature threshold limit in the remote 4 alert high limit register. 2 remote alert high 3 0 channel 3 remote-diode high-alert bit. this bit is set to logic 1 when the channel 3 remote-diode temperature exceeds the programmed temperature threshold limit in the remote 3 alert high limit register. 1 remote alert high 2 0 channel 2 remote-diode high-alert bit. this bit is set to logic 1 when the channel 2 remote-diode temperature exceeds the programmed temperature threshold limit in the remote 2 alert high limit register. 0 remote alert high 1 0 channel 1 remote-diode high-alert bit. this bit is set to logic 1 when the channel 1 remote-diode temperature exceeds the programmed temperature threshold limit in the remote 1 alert high limit register. downloaded from: http:///
18 maxim integrated 1c accurate 8-channel temperature sensor max6581 table 8. overt status register (45h) table 9. diode fault status register (46h) bit name por state function 7 (msb) remote overt 7 0 channel 7 remote-diode overtemperature status bit. this bit is set to logic 1 when the channel 7 remote-diode temperature exceeds the temperature threshold limit in the remote 7 overt high limit register. 6 local overt 0 local channel overtemperature status bit. this bit is set to logic 1 when the local temperature exceeds the temperature threshold limit in the local overt high limit register. 5 remote overt 6 0 channel 6 remote-diode overtemperature status bit. this bit is set to logic 1 when the channel 6 remote-diode temperature exceeds the temperature threshold limit in the remote 6 overt high limit register. 4 remote overt 5 0 channel 5 remote-diode overtemperature status bit. this bit is set to logic 1 when the channel 5 remote-diode temperature exceeds the temperature threshold limit in the remote 5 overt high limit register. 3 remote overt 4 0 channel 4 remote-diode overtemperature status bit. this bit is set to logic 1 when the channel 4 remote-diode temperature exceeds the temperature threshold limit in the remote 4 overt high limit register. 2 remote overt 3 0 channel 3 remote-diode overtemperature status bit. this bit is set to logic 1 when the channel 3 remote-diode temperature exceeds the temperature threshold limit in the remote 3 overt high limit register. 1 remote overt 2 0 channel 2 remote-diode overtemperature status bit. this bit is set to logic 1 when the channel 2 remote-diode temperature exceeds the temperature threshold limit in the remote 2 overt high limit register. 0 remote overt 1 0 channel 1 remote-diode overtemperature status bit. this bit is set to logic 1 when the channel 1 remote-diode temperature exceeds the temperature threshold limit in the remote 1 overt high limit register. bit name por state function 7 (msb) reserved 0 ? 6 diode fault 7 0 channel 7 remote-diode fault bit. this bit is set to 1 when dxp7 and dxn7 are open circuit or when dxp7 is connected to v cc . 5 diode fault 6 0 channel 6 remote-diode fault bit. this bit is set to 1 when dxp6 and dxn6 are open circuit or when dxp6 is connected to v cc . 4 diode fault 5 0 channel 5 remote-diode fault bit. this bit is set to 1 when dxp5 and dxn5 are open circuit or when dxp5 is connected to v cc . 3 diode fault 4 0 channel 4 remote-diode fault bit. this bit is set to 1 when dxp4 and dxn4 are open circuit or when dxp4 is connected to v cc . 2 diode fault 3 0 channel 3 remote-diode fault bit. this bit is set to 1 when dxp3 and dxn3 are open circuit or when dxp3 is connected to v cc . 1 diode fault 2 0 channel 2 remote-diode fault bit. this bit is set to 1 when dxp2 and dxn2 are open circuit or when dxp2 is connected to v cc . 0 diode fault 1 0 channel 1 remote-diode fault bit. this bit is set to 1 when dxp1 and dxn1 are open circuit or when dxp1 is connected to v cc . downloaded from: http:///
19 maxim integrated 1c accurate 8-channel temperature sensor max6581 effect of ideality factor the accuracy of the remote temperature measurements depends on the ideality factor (n) of the remote ?diode? (actually a transistor). the default value for the max6581 is n = 1.008 (channels 1?7). a thermal diode on the substrate of an ic is normally a pnp with the base and emitter brought out and the collector (diode connection) grounded. dxp_ must be connected to the anode (emit - ter) and dxn_ must be connected to the cathode (base) of this pnp. if a sense transistor with an ideality factor other than 1.008 is used, the output data is different from the data obtained with the optimum ideality factor. if necessary, a different ideality factor value can be chosen using the transistor ideality register (see table 11). the ideality select register allows each channel to have the default ideality of 1.008 or the value programmed in the transistor ideality register. table 10. alert low status register (47h) bit name por state function 7 (msb) remote alert low 7 0 channel 7 remote-diode low-alert bit. this bit is set to logic 1 when the channel 7 remote-diode temperature falls below the programmed temperature threshold limit in the remote 7 alert low limit register. 6 local alert low 0 local channel remote-diode low-alert bit. this bit is set to logic 1 when the local channel remote-diode temperature falls below the programmed temperature threshold limit in the local alert low limit register. 5 remote alert low 6 0 channel 6 remote-diode low-alert bit. this bit is set to logic 1 when the channel 6 remote-diode temperature falls below the programmed temperature threshold limit in the remote 6 alert low limit register. 4 remote alert low 5 0 channel 5 remote-diode low-alert bit. this bit is set to logic 1 when the channel 5 remote-diode temperature falls below the programmed temperature threshold limit in the remote 5 alert low limit register. 3 remote alert low 4 0 channel 4 remote-diode low-alert bit. this bit is set to logic 1 when the channel 4 remote-diode temperature falls below the programmed temperature threshold limit in the remote 4 alert low limit register. 2 remote alert low 3 0 channel 3 remote-diode low-alert bit. this bit is set to logic 1 when the channel 3 remote-diode temperature falls below the programmed temperature threshold limit in the remote 3 alert low limit register. 1 remote alert low 2 0 channel 2 remote-diode low-alert bit. this bit is set to logic 1 when the channel 2 remote-diode temperature falls below the programmed temperature threshold limit in the remote 2 alert low limit register. 0 remote alert low 1 0 channel 1 remote-diode low-alert bit. this bit is set to logic 1 when the channel 1 remote-diode temperature falls below the programmed temperature threshold limit in the remote 1 alert low limit register. downloaded from: http:///
20 maxim integrated 1c accurate 8-channel temperature sensor max6581 table 11. transistor ideality register x = don?t care. register b7 b6 b5 b4 b3 b2 b1 b0 ideality factor hex 0x4b x x x 0 0 0 0 0 .999 0x00 x x x 0 0 0 0 1 1.000 0x01 x x x 0 0 0 1 0 1.001 0x02 x x x 0 0 0 1 1 1.002 0x03 x x x 0 0 1 0 0 1.003 0x04 x x x 0 0 1 0 1 1.004 0x05 x x x 0 0 1 1 0 1.005 0x06 x x x 0 0 1 1 1 1.006 0x07 x x x 0 1 0 0 0 1.007 0x08 x x x 0 1 0 0 1 1.008 0x09 x x x 0 1 0 1 0 1.009 0x0a x x x 0 1 0 1 1 1.010 0x0b x x x 0 1 1 0 0 1.011 0x0c x x x 0 1 1 0 1 1.012 0x0d x x x 0 1 1 1 0 1.013 0x0e x x x 0 1 1 1 1 1.014 0x0f x x x 1 0 0 0 0 1.015 0x10 x x x 1 0 0 0 1 1.016 0x11 x x x 1 0 0 1 0 1.017 0x12 x x x 1 0 0 1 1 1.018 0x13 x x x 1 0 1 0 0 1.019 0x14 x x x 1 0 1 0 1 1.020 0x15 x x x 1 0 1 1 0 1.021 0x16 x x x 1 0 1 1 1 1.022 0x17 x x x 1 1 0 0 0 1.023 0x18 x x x 1 1 0 0 1 1.024 0x19 x x x 1 1 0 1 0 1.025 0x1a x x x 1 1 0 1 1 1.026 0x1b x x x 1 1 1 0 0 1.027 0x1c x x x 1 1 1 0 1 1.028 0x1d x x x 1 1 1 1 0 1.029 0x1e x x x 1 1 1 1 1 1.030 0x1f downloaded from: http:///
21 maxim integrated 1c accurate 8-channel temperature sensor max6581 series-resistance cancellation some thermal diodes on high-power ics have exces - sive series resistance that can cause temperature-mea - surement errors when used with conventional remote-temperature sensors. channels 1?7 of the max6581 have a series-resistance cancellation feature (enabled by bits [7:0] of the resistance cancellation register) that eliminates the effect of diode series resistance and interconnection resistance. set these bits to 1 if the series resistance is large enough to affect the accuracy of the channels. the series-resistance cancellation function increases the conversion time for the remote channels by 125ms (typ). this feature cancels the bulk resistance of the sensor and any other resistance in series (e.g., wire, contact resistance, etc.). the cancellation range is from 0 i to 100 i . table 12. resistance cancellation register (4ah) x = don?t care. bit name por state function 7 (msb) x 0 ? 6 resistance cancellation 7 0 channel 7 resistance cancellation enable bit. set this bit to logic 1 to enable resistance cancellation. set this bit to logic 0 to disable resistance cancellation. 5 resistance cancellation 6 0 channel 6 resistance cancellation enable bit. set this bit to logic 1 to enable resistance cancellation. set this bit to logic 0 to disable resistance cancellation. 4 resistance cancellation 5 0 channel 5 resistance cancellation enable bit. set this bit to logic 1 to enable resistance cancellation. set this bit to logic 0 to disable resistance cancellation. 3 resistance cancellation 4 0 channel 4 resistance cancellation enable bit. set this bit to logic 1 to enable resistance cancellation. set this bit to logic 0 to disable resistance cancellation. 2 resistance cancellation 3 0 channel 3 resistance cancellation enable bit. set this bit to logic 1 to enable resistance cancellation. set this bit to logic 0 to disable resistance cancellation. 1 resistance cancellation 2 0 channel 2 resistance cancellation enable bit. set this bit to logic 1 to enable resistance cancellation. set this bit to logic 0 to disable resistance cancellation. 0 resistance cancellation 1 0 channel 1 resistance cancellation enable bit. set this bit to logic 1 to enable resistance cancellation. set this bit to logic 0 to disable resistance cancellation. downloaded from: http:///
22 maxim integrated 1c accurate 8-channel temperature sensor max6581 offset and offset select registers (4dh and 4eh) to compensate for remote temperature reporting errors due to issues with the board layout, the offset register (4dh) and offset enable register (4eh) allow for a two?s- complement value to be added to the final adc conver - sion output. the offset register (4dh) contains the value for the shared temperature offset (i.e., the same offset is applied to all selected remote channels) and has a programmable 31.75c range. the offset enable register (4eh) allows the offset to be selectively enabled for each remote channel. if extrange = 0, the minimum digital output values are clamped at 00h (0c), regardless of any applied offset. if extrange = 1, the maximum digital output values are clamped at ffh (+191c), regardless of any applied offset. table 13. offset register (4dh)table 14. offset select register (4eh) bit name por state function 7 (msb) sign 0 digital offset polarity 6 16 c 0 digital offset (weighted) 5 8 c 0 digital offset (weighted) 4 4 c 0 digital offset (weighted) 3 2 c 0 digital offset (weighted) 2 1 c 0 digital offset (weighted) 1 0.5 c 0 digital offset (weighted) 0 0.25 c 0 digital offset (weighted) bit name por state function 7 (msb) x 0 ? 6 channel 7 0 remote 7 offset enable 5 channel 6 0 remote 6 offset enable 4 channel 5 0 remote 5 offset enable 3 channel 4 0 remote 4 offset enable 2 channel 3 0 remote 3 offset enable 1 channel 2 0 remote 2 offset enable 0 channel 1 0 remote 1 offset enable downloaded from: http:///
23 maxim integrated 1c accurate 8-channel temperature sensor max6581 applications information remote-diode selection the max6581 directly measures the die temperature of cpus and other ics that have on-chip temperature-sensing diodes (see the typical application circuit ), or it can measure the temperature of a discrete diode-connected transistor. discrete remote diodes when the remote-sensing diode is a discrete transistor, its collector and base must be connected together. table 13 lists examples of discrete transistors that are appro - priate for use with the max6581. the transistor must be a small-signal type with a relatively high forward voltage; otherwise, the a/d input-voltage range can be violated. the forward voltage at the highest expected temperature must be greater than 0.25v at 10 f a, and at the low - est expected temperature the forward voltage must be less than 0.95v at 100 f a. large power transistors must not be used. also, ensure that the base resistance is less than 100 i . tight specifications for forward-current gain (e.g., 50 < a < 150) indicate that the manufacturer has good process controls and that the devices have consistent v be characteristics. manufacturers of discrete transistors do not normally specify or guarantee ideality factor. this normally is not a problem since good-quality discrete transistors tend to have ideality factors that fall within a relatively narrow range. variations in remote temperature readings of less than q 2 n c with a variety of discrete transistors have been observed. however, it is good design practice to verify good consistency of tem - perature readings with several discrete transistors from any supplier under consideration. unused diode channels if one or more of the remote-diode channels is not need - ed, disconnect the dxp_ and dxn_ inputs for that chan - nel, or connect the dxp_ to the corresponding dxn_. the status register indicates a diode ?fault? for this channel and the channel is ignored during the tempera - ture-measurement sequence. it is also good practice to mask any unused channels immediately upon power-up by setting the appropriate bits in the alert mask and overt mask registers. this prevents unused channels from causing alert or overt to assert. table 15. remote sensors transistor suppliers (for channels 1?7)note: discrete transistors must be diode connected (base shorted to collector). supplier model no. pnp npn central semiconductor corp. (usa) cmpt3906 2n3906 cmpt3904 2n3904 fairchild semiconductor (usa) mmbt3906 2n3906 2n3904 infineon (germany) smbt3906 ? on semiconductor (usa) mmbt3906 2n3906 2n3904 rohm semiconductor (usa) sst3906 sst3904 samsung (korea) kst3906-tf kst3904-tf siemens (germany) smbt3906 smbt3904 zetex (england) fmmt3906ct-nd fmmt3904ct-nd downloaded from: http:///
24 maxim integrated 1c accurate 8-channel temperature sensor max6581 thermal mass and self-heating when sensing local temperature, the max6581 mea - sures the temperature of the pcb to which it is soldered. the leads provide a good thermal path between the pcb traces and the die. as with all ic temperature sensors, thermal conductivity between the die and the ambient air is poor by comparison, making air-temperature mea - surements impractical. since the thermal mass of the pcb is far greater than that of the max6581, the device follows temperature changes on the pcb with little or no perceivable delay. when measuring the temperature of a cpu, or other ic with an on-chip sense junction, thermal mass has virtually no effect; the measured temperature of the junction tracks the actual temperature within a conversion cycle. when measuring temperature with discrete remote transistors, the best thermal-response times are obtained with transistors in small packages (i.e., sot23 or sc70). take care to account for thermal gradients between the heat source and the sensor, and ensure that stray air currents across the sensor package do not interfere with measurement accuracy. self-heating does not significantly affect measurement accuracy. remote-sensor self-heating due to the diode current source is negligible. adc noise filtering the integrating adc has good noise rejection for low-frequency signals, such as power-supply hum. in envi - ronments with significant high-frequency emi, connect an external 100pf capacitor between dxp_ and dxn_. larger capacitor values can be used for added filter - ing; however, it can introduce errors due to the rise time of the switched current source. high-frequency noise reduction is needed for high-accuracy remote measure - ments. noise can be reduced with careful pcb layout as discussed in the pcb layout section. slave address the slave address for the max6581 is shown in table 16. pcb layout follow the guidelines below to reduce the measurement error when measuring remote temperature: 1) place the max6581 as close as possible to the remote diode. in noisy environments, such as a com - puter motherboard, this distance is typically 4in to 8in. this length can be increased if the worst-noise sources are avoided. noise sources include displays, clock generators, memory buses, and pci buses. 2) do not route the dxp_?dxn_ lines next to the deflec - tion coils of a crt. also, do not route the traces across fast digital signals, which can easily introduce +30 n c error, even with good filtering. 3) route the dxp_ and dxn_ traces in parallel and in close proximity to each other. each parallel pair of traces should go to a remote diode. route these traces away from any higher voltage traces, such as +12v dc. leakage currents from pcb contamination must be dealt with carefully since a 20m i leakage path from dxp_ to ground causes approximately +1 n c error. if high-voltage traces are unavoidable, connect guard traces to gnd on either side of the dxp_?dxn_ traces (figure 5). 4) route through as few vias and crossunders as possi - ble to minimize copper/solder thermocouple effects. 5) use wide traces when possible (5-mil to 10-mil traces are typical). be aware of the effect of trace resistance on temperature readings when using long, narrow traces. 6) when the power supply is noisy, add a resistor (up to 47 i ) in series with v cc . figure 5. recommended dxp_?dxn_ pcb traces. the two outer guard traces are recommended if high-voltage traces are near the dxn_ and dxp_ traces. table 16. slave address 5?10 mils 5?10 mils 5?10 milsminimum 5?10 mils gnd dxp_ dxn_ gnd device address a7 a6 a5 a4 a3 a2 a1 a0 1 0 0 1 1 0 1 r/ w downloaded from: http:///
25 maxim integrated 1c accurate 8-channel temperature sensor max6581 twisted-pair and shielded cables use a twisted-pair cable to connect the remote sensor for remote-sensor distances longer than 8in or in very noisy environments. twisted-pair cable lengths can be between 6ft and 12ft before noise introduces exces - sive errors. for longer distances, the best solution is a shielded twisted pair such as those 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 cables to dxp_ and dxn_ and the shielded cable to gnd. leave the shielded cable unconnected at the remote sensor. for very long cable runs, the cable?s parasitic capacitance often provides noise filtering; therefore the 100pf capacitor can often be removed or reduced in value. cable resistance also affects remote-sensor accuracy. for every 1 i of series resistance, the error is approximately +0.5 n c. typical application circuit dxp2 alert v cc overt stby dxp7 i.c. 24 23 22 21 20 19 1817 16 15 14 13 12 dxn2 12 dxp1 n.c. gnd +3.3v smbclk smbdata cpu fpga asic 100pf 100pf dxp3dxn3 dxn1 dxn7 34 5 6 100pf100pf 100pf 100pf 10 11 dxn6 dxp6 8 79 dxp5 dxn4 dxn5 4.7k i 4.7k i 4.7k i 4.7k i to p to p to p to p 0.1 f dxp4n.c. max6581 downloaded from: http:///
26 maxim integrated 1c accurate 8-channel temperature sensor max6581 chip information process: bicmos package information for the latest package outline information and land patterns, go to www.maximintegrated.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. package type package code outline no. land pattern no. 24 tqfn-ep t2444+4 21-0139 90-0022 downloaded from: http:///
maxim integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim integrated product. no circuit patent licenses are implied. maxim integrated 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. maxim integrated 160 rio robles, san jose, ca 95134 usa 1-408-601-1000 27 ? 2013 maxim integrated maxim integrated and the maxim integrated logo are trademarks of maxim integrated products, inc. 1c accurate 8-channel temperature sensor max6581 revision history revision number revision date description pages changed 0 8/10 initial release ? 1 2/13 added the package thermal characteristics section; updated table 1; added 58h register to table 3; added the offset and offset select registers (4dh and 4eh) section and related bit tables 2, 12, 14, 22 downloaded from: http:///

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