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________________general description the max1668/max1805/MAX1989 are precise multi- channel digital thermometers that report the tempera- ture of all remote sensors and their own packages. the remote sensors are diode-connected transistors?ypi- cally low-cost, easily mounted 2n3904 npn types?hat replace conventional thermistors or thermocouples. remote accuracy is ?? for multiple transistor manu- facturers, with no calibration needed. the remote chan- nels can also measure the die temperature of other ics, such as microprocessors, that contain an on-chip, diode-connected transistor. the 2-wire serial interface accepts standard system management bus (smbus) write byte, read byte, send byte, and receive byte commands to program the alarm thresholds and to read temperature data. the data for- mat is 7 bits plus sign, with each bit corresponding to 1?, in two?-complement format. the max1668/max1805/MAX1989 are available in small, 16-pin qsop surface-mount packages. the MAX1989 is also available in a 16-pin tssop. ________________________applications ____________________________features multichannel 4 remote, 1 local (max1668/MAX1989) 2 remote, 1 local (max1805) no calibration required smbus 2-wire serial interface programmable under/overtemperature alarms supports smbus alert response accuracy ?? (+60? to +100?, local) ?? (-40? to +125?, local) ?? (+60? to +100?, remote) 3? (typ) standby supply current 700? (max) supply current small, 16-pin qsop/tssop packages max1668/max1805/MAX1989 ? multichannel remote/local temperature sensors ________________________________________________________________ maxim integrated products 1 smbclk add0 add1 v cc stby gnd alert smbdata dxp1 dxp4 dxn4 interrupt to c 3v to 5.5v 200? 0.1f clock 10k? each data dxn1 2200pf 2200pf * diode-connected transistor * * max1668 max1805 MAX1989 pin configuration 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 dxp1 gnd stby smbclk smbdata alert add0 add1 v cc top view max1668 max1805 MAX1989 qsop/tssop dxn1 dxp2 (n.c.) dxn3 dxn2 (n.c.) dxp3 (n.c.) dxp4 ( ) are for max1805. (n.c.) dxn4 typical operating circuit 19-1766; rev 2; 5/03 part max1668mee -55? to +125? temp range pin-package 16 qsop _______________ordering information smbus is a trademark of intel corp. ?pg max1805mee -55? to +125? 16 qsop desktop and notebook computers lan servers industrial controls central-office telecom equipment test and measurement multichip modules MAX1989mee -55? to +125? 16 qsop for pricing, delivery, and ordering information, please contact maxim/dallas direct! at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. MAX1989mue -55? to +125? 16 tssop
max1668/max1805/MAX1989 ? multichannel remote/local temperature sensors 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v cc = +3.3v, stby = v cc , configuration byte = x0xxxx00, t a = 0c to +125c, unless otherwise noted.) stresses beyond those listed under ?bsolute 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. v cc to gnd ..............................................................-0.3v to +6v dxp_, add_, stby to gnd........................-0.3v to (v cc + 0.3v) dxn_ to gnd ........................................................-0.3v to +0.8v smbclk, smbdata, alert to gnd ......................-0.3v to +6v smbdata, alert current .................................-1ma to +50ma dxn_ current......................................................................?ma continuous power dissipation (t a = +70?) qsop (derate 8.30mw/? above +70?) ....................667mw tssop (derate 9.40mw/? above +70?) ..................755mw operating temperature range .........................-55? to +125? junction temperature ......................................................+150? storage temperature range .............................-65? to +150? lead temperature (soldering, 10s) .................................+300? dxp_ forced to 1.5v remote-diode source current low level (por state) configuration byte = x0xxxx10, high level configuration byte = x0xxxx01, high level high level (por state) 71013 200 50 dxn_ source voltage 0.7 v hardware or software standby, smbclk at 10khz smbus static t a = 0? to +85? t a = +60? to +100? average measured over 4s; logic inputs forced v cc or gnd temperature error, local diode (notes 1, 2) -3.5 +3.5 ? -2.5 +2.5 including long-term drift temperature error, remote diode (notes 2, 3) -5 +5 ? -3 +3 t r = -55? to +125? t r = +60? to +100? parameter min typ max units undervoltage lockout hysteresis 50 mv undervoltage lockout threshold 2.60 2.8 2.95 v supply voltage range 3.0 5.5 v initial temperature error, local diode (note 2) -3 +3 ? power-on reset (por) threshold 1.3 1.8 2.3 v por threshold hysteresis 50 mv 310 standby supply current 512 ? temperature resolution (note 1) 8 bits -2 +2 average operating supply current 400 700 ? conversion time 260 320 380 ms 70 100 130 ? address pin bias current 160 ? conditions v cc input, disables a/d conversion, rising edge t a = 0? to +125? v cc , falling edge from stop bit to conversion complete (all channels) logic inputs forced to v cc or gnd add0, add1; momentary upon power-on reset monotonicity guaranteed t a = +60? to +100? adc and power supply
max1668/max1805/MAX1989 ? multichannel remote/local temperature sensors _______________________________________________________________________________________ 3 electrical characteristics (continued) (v cc = +3.3v, stby = v cc , configuration byte = x0xxxx00, t a = 0c to +125c, unless otherwise noted.) stby, smbclk, smbdata; v cc = 3v to 5.5v t high , 90% to 90% points t low , 10% to 10% points (note 4) smbclk, smbdata logic inputs forced to v cc or gnd alert forced to 5.5v stby, smbclk, smbdata; v cc = 3v to 5.5v alert, smbdata forced to 0.4v conditions ? 4 smbclk clock high time ? 4.7 smbclk clock low time khz dc 100 smbus clock frequency pf 5 smbus input capacitance ? -1 +1 logic input current ? 1 alert output high leakage current v 2.2 logic input high voltage v 0.8 logic input low voltage ma 6 logic output low sink current units min typ max parameter t su:dat , 10% or 90% of smbdata to 10% of smbclk t su:sto , 90% of smbclk to 10% of smbdata t hd:sta , 10% of smbdata to 90% of smbclk t su:sta , 90% to 90% points ns 250 smbus data valid to smbclk rising-edge time ? 4 smbus stop-condition setup time ? 4 smbus start-condition hold time ns 250 smbus repeated start-condition setup time ? 4.7 smbus start-condition setup time ns smbus data-hold time master clocking in data ? 1 smbclk falling edge to smbus data-valid time smbus interface electrical characteristics (v cc = +5v, stby = v cc , configuration byte = x0xxxx00, t a = -55c to +125c, unless otherwise noted.) (note 6) conditions monotonicity guaranteed t a = +60? to +100? bits 8 temperature resolution -2 +2 t r = +60? to +100? t a = -55? to +125? ? -3 +3 initial temperature error, local diode (note 2) v 4.5 5.5 supply-voltage range from stop bit to conversion complete (both channels) ms 260 380 conversion time -3 +3 t r = -55? to +125? ? units min typ max -5 +5 parameter temperature error, remote diode (notes 2, 3) adc and power supply t hd:dat , slave receive (note 5) 0
0 8 4 16 12 20 24 max1668/1805 toc03 frequency (mhz) temperature error ( c) temperature error vs. supply noise frequency 100mv p-p 0.1 1 10 100 with v cc 0.1f capacitor removed 2200pf between dxn_ and dxp_ 250mv p-p 20 -20 1 10 100 temperature error vs. pc board resistance -10 max1668/1805 toc01 leakage resistance (m ?) temperature error ( c) 0 10 path = dxp_ to gnd path = dxp_ to v cc (5v) -2 -1 0 1 2 3 4 -50 -10 -30 1030507090110 temperature error vs. temperature max1668/1805 toc02 temperature (c) temperature error ( c) npn (cmpt3904) pnp (cmpt3906) internal typical operating characteristics (typical operating circuit, v cc = +5v, stby = v cc , configuration byte = x0xxxx00, t a = +25?, unless otherwise noted.) max1668/max1805/MAX1989 ? multichannel remote/local temperature sensors 4 _______________________________________________________________________________________ electrical characteristics (continued) (v cc = +5v, stby = v cc , configuration byte = x0xxxx00, t a = -55c to +125c, unless otherwise noted.) (note 6) note 1: guaranteed by design, but not production tested. note 2: quantization error is not included in specifications for temperature accuracy. for example, if the max1668/max1805/ MAX1989 device temperature is exactly +66.7?, the adc may report +66?, +67?, or +68? (due to the quantization error plus the +0.5? offset used for rounding up) and still be within the guaranteed ?? error limits for the +60? to +100? temperature range. see table 2. note 3: a remote diode is any diode-connected transistor from table 1. t r is the junction temperature of the remote diode. see the remote-diode selection section for remote-diode forward-voltage requirements. note 4: the smbus logic block is a static design that works with clock frequencies down to dc. while slow operation is possible, it violates the 10khz minimum clock frequency and smbus specifications, and can monopolize the bus. note 5: note that a transition must internally provide at least a hold time in order to bridge the undefined region (300ns max) of smbclk? falling edge t hd:dat. note 6: specifications from -55? to +125? are guaranteed by design, not production tested. conditions units min typ max parameter stby, smbclk, smbdata; v cc = 4.5v to 5.5v logic input high voltage v 2.4 alert forced to 5.5v ? 1 alert output high leakage current logic inputs forced to v cc or gnd ? -2 +2 logic input current alert, smbdata forced to 0.4v ma 6 logic output low sink current stby, smbclk, smbdata; v cc = 4.5v to 5.5v v 0.8 logic input low voltage smbus interface
0 20 40 60 80 100 120 140 160 012345 standby supply current vs. supply voltage max1668/1805 toc07 supply voltage (v) supply current (a) stby = gnd add0 = add1 = high-z add0 = add1 = gnd 0 25 75 50 100 125 -2 2 0468 response to thermal shock max1668/1805 toc08 time (s) temperature (c) 16 qsop immersed in +115c fluorinert bath max1668/max1805/MAX1989 ? multichannel remote/local temperature sensors _______________________________________________________________________________________ 5 0.1 1 1000 temperature error vs. common-mode noise frequency max1668/1805 toc04 frequency (mhz) temperature error ( c) 10 100 0 0.6 0.4 0.2 0.8 1.0 1.2 1.4 1.6 1.8 2.0 square-wave ac-coupled into dxn 2200pf between dxn_ and dxp_ 100mv p-p 50mv p-p typical operating characteristics (continued) (typical operating circuit, v cc = +5v, stby = v cc , configuration byte = x0xxxx00, t a = +25?, unless otherwise noted.) temperature error vs. dxp_ to dxn_ capacitance max16681805 toc05 dxp_ to dxn_ capacitance (nf) temperature error ( c) -10 -6 -8 -2 -4 2 0 4 02030 10 40 50 60 standby supply current vs. clock frequency max1668/1805 toc06 smbclk frequency (khz) supply current (a) 60 0 10 20 30 40 50 1 10 100 1000 stby = gnd v cc = 5v v cc = 3.3v
max1668/max1805/MAX1989 ? multichannel remote/local temperature sensors 6 _______________________________________________________________________________________ _______________detailed description the max1668/max1805/MAX1989 are temperature sensors designed to work in conjunction with an exter- nal microcontroller (?) or other intelligence in thermo- static, process-control, or monitoring applications. the ? is typically a power-management or keyboard con- troller, generating smbus serial commands by ?it- banging?general-purpose input-output (gpio) pins or through a dedicated smbus interface block. these devices are essentially 8-bit serial analog-to-digi- tal converters (adcs) with sophisticated front ends. however, the max1668/max1805/MAX1989 also contain a switched current source, a multiplexer, an adc, an smbus interface, and associated control logic (figure 1). in the max1668 and MAX1989, temperature data from the adc is loaded into five data registers, where it is automatically compared with data previously stored in 10 over/undertemperature alarm registers. in the max1805, temperature data from the adc is loaded into three data registers, where it is automatically compared with data previously stored in six over/undertemperature alarm registers. adc and multiplexer the adc is an averaging type that integrates over a 64ms period (each channel, typical), with excellent noise rejection. the multiplexer automatically steers bias currents through the remote and local diodes, measures their forward voltages, and computes their temperatures. each channel is automatically converted once the con- version process has started. if any one of the channels is not used, the device still performs measurements on these channels, and the user can ignore the results of the unused channel. if any remote-diode channel is unused, connect dxp_ to dxn_ rather than leaving the pins open. the dxn_ input is biased at 0.65v above ground by an internal diode to set up the a/d inputs for a differential measurement. the worst-case dxp_ to dxn_ differential input voltage range is 0.25v to 0.95v. excess resistance in series with the remote diode caus- es about +0.5? error per ohm. likewise, 200? of offset voltage forced on dxp_ to dxn_ causes about 1? error. max1668/ MAX1989 function 1, 3, 5, 7 dxp_ combined current source and a/d positive input for remote-diode channel. do not leave dxp floating; connect dxp to dxn if no remote diode is used. place a 2200pf capacitor between dxp and dxn for noise filtering. pin 12 alert smbus alert (interrupt) output, open drain 11 add0 smbus slave address select pin 10 add1 smbus address select pin (table 8). add0 and add1 are sampled upon power-up. excess capacitance (>50pf) at the address pins when floating can cause address- recognition problems. 15 stby hardware standby input. temperature and comparison threshold data are retained in standby mode. low = standby mode, high = operate mode. 14 smbclk smbus serial-clock input 13 smbdata smbus serial-data input/output, open drain 1, 3 12 11 10 15 14 13 pin description name max1805 2, 4, 6, 8 dxn_ combined current sink and a/d negative input. dxn is normally biased to a diode volt- age above ground. 2, 4 9 v cc supply voltage input, 3v to 5.5v. bypass to gnd with a 0.1? capacitor. a 200 ? series resistor is recommended but not required for additional noise filtering. 9 16 gnd ground 16 n.c. no connection. not internally connected. can be used for pc board trace routing. 5?
max1668/max1805/MAX1989 ? multichannel remote/local temperature sensors _______________________________________________________________________________________ 7 figure 1. max1668/max1805/MAX1989 functional diagram dxp4 dxp3 dxp2 dxp1 dxn4 dxn3 dxn2 dxn1 local current sources mux diode fault adc control logic smbus address decoder stby add add1 smbdata smbclk alert q r s digital comparators alert response configuration byte address register register status byte registers 1 and 2 command byte register temperature data registers high limits registers low limits registers alert mask register note: dotted lines are for max1668 and MAX1989.
a/d conversion sequence if a start command is written (or generated automatically in the free-running autoconvert mode), all channels are converted, and the results of all measurements are available after the end of conversion. a busy status bit in the status byte shows that the device is actually per- forming a new conversion; however, even if the adc is busy, the results of the previous conversion are always available. remote-diode selection temperature accuracy depends on having a good-qual- ity, diode-connected small-signal transistor. accuracy has been experimentally verified for all of the devices listed in table 1. the max1668/max1805/MAX1989 can also directly measure the die temperature of cpus and other ics having on-board temperature-sensing diodes. the transistor must be a small-signal type, either npn or pnp, with a relatively high forward voltage; other- wise, the a/d input voltage range can be violated. the forward voltage must be greater than 0.25v at 10?; check to ensure this is true at the highest expected temperature. the forward voltage must be less than 0.95v at 100?; check to ensure this is true at the low- est expected temperature. large power transistors do not work at all. also, ensure that the base resistance is less than 100?. tight specifications for forward-current gain (+50 to +150, for example) indicate that the manu- facturer has good process controls and that the devices have consistent vbe characteristics. for heat-sink mounting, the 500-32bt02-000 thermal sensor from fenwal electronics is a good choice. this device consists of a diode-connected transistor, an aluminum plate with screw hole, and twisted-pair cable (fenwal inc., milford, ma, 508-478-6000). thermal mass and self-heating thermal mass can seriously degrade the max1668/ max1805/MAX1989s?effective accuracy. the thermal time constant of the 16-pin qsop package is about 140s in still air. for the max1668/max1805/MAX1989 junction temperature to settle to within +1? after a sudden +100? change requires about five time con- stants or 12 minutes. the use of smaller packages for remote sensors, such as sot23s, improves the situa- tion. take care to account for thermal gradients between the heat source and the sensor, and ensure that stray air currents across the sensor package do not interfere with measurement accuracy. self-heating does not significantly affect measurement accuracy. remote-sensor self-heating due to the diode current source is negligible. for the local diode, the worst-case error occurs when sinking maximum current at the alert output. for example, with alert sinking 1ma, the typical power dissipation is v cc x 400? plus 0.4v x 1ma. package theta j-a is about 150?/w, so with v cc = 5v and no copper pc board heat sinking, the resulting temperature rise is: dt = 2.4mw x 150?/w = 0.36? even with these contrived circumstances, it is difficult to introduce significant self-heating errors. adc noise filtering the adc is an integrating type with inherently good noise rejection, especially of low-frequency signals such as 60hz/120hz power-supply hum. micropower opera- tion places constraints on high-frequency noise rejec- tion; therefore, careful pc board layout and proper external noise filtering are required for high-accuracy remote measurements in electrically noisy environments. high-frequency emi is best filtered at dxp_ and dxn_ with an external 2200pf capacitor. this value can be increased to about 3300pf (max), including cable capacitance. higher capacitance than 3300pf intro- duces errors due to the rise time of the switched cur- rent source. nearly all noise sources tested cause additional error measurements, typically by +1? to +10?, depending on the frequency and amplitude (see the typical operating characteristics ). pc board layout 1) place the max1668/max1805/MAX1989 as close as practical to the remote diode. in a noisy environment, such as a computer motherboard, this distance can max1668/max1805/MAX1989 ? multichannel remote/local temperature sensors 8 _______________________________________________________________________________________ cmpt3904 central semiconductor (usa) mmbt3904 motorola (usa) mmbt3904 sst3904 rohm semiconductor (japan) kst3904-tf samsung (korea) fmmt3904ct-nd zetex (england) manufacturer model no. smbt3904 siemens (germany) table 1. remote-sensor transistor manufacturers note: transistors must be diode connected (base shorted to collector). national semiconductor (usa)
be 4in to 8in (typ) or more as long as the worst noise sources (such as crts, clock generators, memory buses, and isa/pci buses) are avoided. 2) do not route the dxp_ to dxn_ lines next to the deflection coils of a crt. also, do not route the traces across a fast memory bus, which can easily introduce +30? error, even with good filtering. otherwise, most noise sources are fairly benign. 3) route the dxp_ and dxn_ traces in parallel and in close proximity to each other, away from any high- voltage traces such as +12vdc. leakage currents from pc board contamination must be dealt with carefully, since a 20m? leakage path from dxp_ to ground causes about +1? error. 4) connect guard traces to gnd on either side of the dxp_ to dxn_ traces (figure 2). with guard traces in place, routing near high-voltage traces is no longer an issue. 5) route through as few vias and crossunders as possi- ble to minimize copper/solder thermocouple effects. 6) when introducing a thermocouple, make sure that both the dxp_ and the dxn_ paths have matching thermocouples. in general, pc board-induced ther- mocouples are not a serious problem. a copper-sol- der thermocouple exhibits 3?/?, and it takes about 200? of voltage error at dxp_ to dxn_ to cause a +1? measurement error. so, most para- sitic thermocouple errors are swamped out. 7) use wide traces. narrow ones are more inductive and tend to pick up radiated noise. the 10mil widths and spacings recommended in figure 2 are not absolutely necessary (as they offer only a minor improvement in leakage and noise), but try to use them where practical. 8) copper cannot be used as an emi shield, and only ferrous materials such as steel work well. placing a copper ground plane between the dxp_ to dxn_ traces and traces carrying high-frequency noise sig- nals does not help reduce emi. pc board layout checklist place the max1668/max1805/MAX1989 as close as possible to the remote diodes. keep traces away from high voltages (+12v bus). keep traces away from fast data buses and crts. use recommended trace widths and spacings. place a ground plane under the traces. use guard traces flanking dxp_ and dxn_ and con- necting to gnd. place the noise filter and the 0.1? v cc bypass capacitors close to the max1668/max1805/ MAX1989. add a 200 ? resistor in series with v cc for best noise filtering (see the typical operating circuit). twisted-pair and shielded cables for remote-sensor distances longer than 8in, or in partic- ularly noisy environments, a twisted pair is recommend- ed. its practical length is 6ft to 12ft (typ) before noise becomes a problem, as tested in a noisy electronics lab- oratory. 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. connect the twisted pair to dxp_ and dxn_ and the shield to gnd, and leave the shield? remote end unterminated. excess capacitance at dx_ _ limits practical remote-sen- sor distances (see the typical operating characteristics). for very long cable runs, the cable? parasitic capaci- tance often provides noise filtering, so the 2200pf capac- itor can often be removed or reduced in value. cable resistance also affects remote-sensor accuracy; 1? series resistance introduces about +0.5? error. low-power standby mode standby mode disables the adc and reduces the sup- ply-current drain to less than 12?. enter standby mode by forcing the stby pin low or through the run/stop bit in the configuration byte register. hardware and software standby modes behave almost identically: all data is retained in memory, and the smb interface is alive and listening for reads and writes. activate hardware standby mode by forcing the stby pin low. in a notebook computer, this line can be con- nected to the system sustat# suspend-state signal. the stby pin low state overrides any software conversion command. if a hardware or software standby command is received while a conversion is in progress, the conver- max1668/max1805/MAX1989 ? multichannel remote/local temperature sensors _______________________________________________________________________________________ 9 minimum 10mils 10mils 10mils 10mils gnd gnd dxn_ dxp_ figure 2. recommended dxp_/dxn_ pc traces
sion cycle is truncated, and the data from that conversion is not latched into either temperature-reading register. the previous data is not changed and remains available. in standby mode, supply current drops to about 3?. at very low supply voltages (under the power-on-reset threshold), the supply current is higher due to the address pin bias currents. it can be as high as 100?, depending on add0 and add1 settings. smbus digital interface from a software perspective, the max1668/max1805/ MAX1989 appear as a set of byte-wide registers that contain temperature data, alarm threshold values, or control bits. a standard smbus 2-wire serial interface is used to read temperature data and write control bits and alarm threshold data. each a/d channel within the devices responds to the same smbus slave address for normal reads and writes. the max1668/max1805/MAX1989 employ four standard smbus protocols: write byte, read byte, send byte, and receive byte (figure 3). the shorter receive byte protocol allows quicker transfers, provided that the correct data register was previously selected by a read byte instruc- tion. use caution with the shorter protocols in multimaster systems, since a second master could overwrite the com- mand byte without informing the first master. the temperature data format is 7 bits plus sign in two?-com- plement form for each channel, with each data bit represent- ing 1? (table 2), transmitted msb first. measurements are offset by +0.5? to minimize internal rounding errors; for example, +99.6? is reported as +100?. alarm threshold registers ten (six for max1805) registers store alarm threshold data, with high-temperature (t high ) and low-tempera- ture (t low ) registers for each a/d channel. if either measured temperature equals or exceeds the corre- sponding alarm threshold value, an alert interrupt is asserted. the power-on-reset (por) state of all t high registers of the max1668 and max1805 is full scale (0111 1111, or +127?). the por state of the channel 1 t high register of the MAX1989 is 0110 1110 or +110?, while all other channels are at +127?. the por state of all t low reg- isters is 1100 1001 or -55?. max1668/max1805/MAX1989 ? multichannel remote/local temperature sensors 10 ______________________________________________________________________________________ ack 7 bits address ack wr 8 bits data ack 1 p 8 bits s command write byte format read byte format send byte format receive byte format slave address: equiva- lent to chip-select line of a 3-wire interface command byte: selects which register you are writing to data byte: data goes into the register set by the command byte (to set thresholds, configuration masks, and sampling rate) ack 7 bits address ack wr s ack 8 bits data 7 bits address rd 8 bits /// p s command slave address: equiva- lent to chip-select line command byte: selects which register you are reading from slave address: repeated due to change in data- flow direction data byte: reads from the register set by the command byte ack 7 bits address wr 8 bits command ack p s ack 7 bits address rd 8 bits data /// p s command byte: sends com- mand with no data data byte: this command only works immediately following a read byte. reads data from the register commanded by that last read byte; also used for smbus alert response return address s = start condition shaded = slave transmission p = stop condition /// = not acknowledged figure 3. smbus protocols
diode fault alarm there is a continuity fault detector at dxp_ that detects whether the remote diode has an open-circuit condi- tion. at the beginning of each conversion, the diode fault is checked, and the status byte is updated. this fault detector is a simple voltage detector; if dxp_ rises above v cc - 1v (typ) due to the diode current source, a fault is detected. note that the diode fault is not checked until a conversion is initiated, so immediately after power-on reset, the status byte indicates no fault is present, even if the diode path is broken. if any remote channel is shorted (dxp_ to dxn_ or dxp_ to gnd), the adc reads 0000 0000 so as not to trip either the t high or t low alarms at their por set- tings. in applications that are never subjected to 0? in normal operation, a 0000 0000 result can be checked to indicate a fault condition in which dxp_ is acciden- tally short circuited. similarly, if dxp_ is short circuited to v cc , the adc reads +127? for all remote and local channels, and the device alarms. a a l l e e r r t t interrupts the alert interrupt output signal is latched and can only be cleared by reading the alert response address. interrupts are generated in response to t high and t low comparisons and when a remote diode is disconnected (for continuity fault detection). the interrupt does not halt automatic conversions; new temperature data continues to be available over the smbus interface after alert is asserted. the interrupt output pin is open drain so that devices can share a common interrupt line. the interrupt rate can never exceed the conversion rate. the interface responds to the smbus alert response address, an interrupt pointer return-address feature (see alert response address section). prior to taking corrective action, always check to ensure that an inter- rupt is valid by reading the current temperature. alert response address the smbus alert response interrupt pointer provides quick fault identification for simple slave devices that lack the complex, expensive logic needed to be a bus master. upon receiving an alert interrupt signal, the host master can broadcast a receive byte transmission to the alert response slave address (0001 100). then any slave device that generated an interrupt attempts to identify itself by putting its own address on the bus (table 3). the alert response can activate several different slave devices simultaneously, similar to the i 2 c general call. if more than one slave attempts to respond, bus arbitra- tion rules apply, and the device with the lower address code wins. the losing device does not generate an acknowledge and continues to hold the alert line low until serviced (implies that the host interrupt input is max1668/max1805/MAX1989 ? multichannel remote/local temperature sensors ______________________________________________________________________________________ 11 table 2. data format (two s complement) table 3. read format for alert response address (0001100) add6 6 provide the current max1668/max1805/MAX1989 slave address that was latched at por (table 8) function add5 5 add4 4 add3 3 add2 2 add1 1 add7 7 (msb) 1 0 (lsb) logic 1 bit name digital output data bits temp (c) rounded temp (c) sign msb lsb +130.00 +127 0 111 1111 +127.00 +127 0 111 1111 +126.50 +127 0 111 1111 +126.00 +126 0 111 1110 +25.25 +25 0 001 1001 +0.50 +1 0 000 0000 +0.25 +0 0 000 0000 +0.00 +0 0 000 0000 -0.25 +0 0 000 0000 -0.50 +0 0 000 0000 -0.75 -1 1 111 1111 -1.00 -1 1 111 1111 -25.00 -25 1 110 0111 -25.50 -25 1 110 0110 -54.75 -55 1 100 1001 -55.00 -55 1 100 1001 -65.00 -65 1 011 1111 -70.00 -65 1 011 1111
level sensitive). successful reading of the alert response address clears the interrupt latch. command byte functions the 8-bit command byte register (table 4) is the master index that points to the various other registers within the max1668/max1805/MAX1989. the register s por state is 0000 0000, so that a receive byte transmission (a protocol that lacks the command byte) that occurs immediately after por returns the current local temper- ature data. max1668/max1805/MAX1989 ? multichannel remote/local temperature sensors 12 ______________________________________________________________________________________ table 4. command byte bit assignments for max1668/max1805/MAX1989 *if the device is in hardware standby mode at por, all temperature registers read 0?. **not available for max1805. register command por state function rit 00h 0000 0000* read local temperature ret1 01h 0000 0000* read remote dx1 temperature ret2 02h 0000 0000* read remote dx2 temperature ret3** 03h 0000 0000* read remote dx3 temperature ret4** 04h 0000 0000* read remote dx4 temperature rs1 05h 0000 0000 read status byte 1 rs2 06h 0000 0000 read status byte 2 rc 07h 0000 0000 read configuration byte rihl 08h 0111 1111 read local t high limit rill 09h 1100 1001 read local t low limit rehl1 0ah 0111 1111 (0110 1110) read remote dx1 t high limit (MAX1989) rell1 0bh 1100 1001 read remote dx1 t low limit rehl2 0ch 0111 1111 read remote dx2 t high limit rell2 0dh 1100 1001 read remote dx2 t low limit rehl3** 0eh 0111 1111 read remote dx3 t high limit rell3** 0fh 1100 1001 read remote dx3 t low limit rehl4** 10h 0111 1111 read remote dx4 t high limit rell4** 11h 1100 1001 read remote dx4 t low limit wc 12h n/a write configuration byte wihl 13h n/a write local t high limit will 14h n/a write local t low limit wehi1 15h n/a write remote dx1 t high limit well1 16h n/a write remote dx1 t low limit wehi2 17h n/a write remote dx2 t high limit well2 18h n/a write remote dx2 t low limit wehi3** 19h n/a write remote dx3 t high limit well3** 1ah n/a write remote dx3 t low limit wehi4** 1bh n/a write remote dx4 t high limit well4** 1ch n/a write remote dx4 t low limit mfg id feh 0100 1101 read manufacture id dev id ffh 0000 0011 (0000 0101) [0000 1011] read device id (for max1805) [for MAX1989]
max1668/max1805/MAX1989 ? multichannel remote/local temperature sensors ______________________________________________________________________________________ 13 manufacturer and device id codes two rom registers provide manufacturer and device id codes. reading the manufacturer id returns 4dh, which is the ascii code m (for maxim). reading the device id returns 03h for max1668, 05h for max1805, and 0bh for MAX1989. if the read word 16-bit smbus protocol is employed (rather than the 8-bit read byte), the least significant byte contains the data and the most significant byte contains 00h in both cases. configuration byte functions the configuration byte register (table 5) is used to mask (disable) interrupts and to put the device in soft- ware standby mode. status byte functions the two status byte registers (tables 6 and 7) indicate which (if any) temperature thresholds have been exceeded. the first byte also indicates whether the adc is converting and whether there is an open circuit in a remote-diode dxp_ to dxn_ path. after por, the normal state of all the flag bits is zero, assuming none of the alarm conditions are present. the status byte is cleared by any successful read of the status byte, unless the fault persists. note that the alert interrupt latch is not automatically cleared when the status flag bit is cleared. when reading the status byte, you must check for inter- nal bus collisions caused by asynchronous adc timing, or else disable the adc prior to reading the status byte (through the run/stop bit in the configuration byte). to check for internal bus collisions, read the status byte. if the least significant 7 bits are ones, discard the data and read the status byte again. the status bits lhigh, llow, rhigh, and rlow are refreshed on the smbus clock edge immediately following the stop con- dition, so there is no danger of losing temperature-relat- ed status data as a result of an internal bus collision. the open status bit (diode continuity fault) is only refreshed at the beginning of a conversion, so open data is lost. the alert interrupt latch is independent of the status byte register, so no false alerts are generated by an internal bus collision. if the thigh and tlow limits are close together, it s possible for both high-temp and low-temp status bits to be set, depending on the amount of time between sta- tus read operations (especially when converting at the fastest rate). in these circumstances, its best not to rely on the status bits to indicate reversals in long-term tem- perature changes and instead use a current tempera- ture reading to establish the trend direction. conversion rate the max1668/max1805/MAX1989 are continuously measuring temperature on each channel. the typical conversion rate is approximately three conversions/s (for both devices). the resulting data is stored in the temperature data registers. slave addresses the max1668/max1805/MAX1989 appear to the smbus as one device having a common address for all adc channels. the device address can be set to one of nine different values by pin-strapping add0 and add1 so that more than one max1668/max1805/ MAX1989 can reside on the same bus without address conflicts (table 8). the address pin states are checked at por only, and the address data stays latched to reduce quiescent supply current due to the bias current needed for high-z state detection. the max1668/max1805/MAX1989 also respond to the smbus alert response slave address (see the alert response address section). por and undervoltage lockout the max1668/max1805/MAX1989 have a volatile memory. to prevent ambiguous power-supply condi- tions from corrupting the data in memory and causing erratic behavior, a por voltage detector monitors v cc and clears the memory if v cc falls below 1.8v (typ, see the electrical characteristics table). when power is first applied and v cc rises above 1.85v (typ), the logic blocks begin operating, although reads and writes at v cc levels below 3v are not recommended. a second v cc comparator, the adc uvlo comparator, prevents the adc from converting until there is sufficient head- room (v cc = 2.8v typ). power-up defaults ? interrupt latch is cleared. ? address select pins are sampled. ? adc begins converting. ? command byte is set to 00h to facilitate quick remote receive byte queries. ? t high and t low registers are set to max and min limits, respectively.
max1668/max1805/MAX1989 ? multichannel remote/local temperature sensors 14 ______________________________________________________________________________________ table 5. configuration byte bit assignments table 7. status byte 2 bit assignments table 6. status byte bit 1 assignments note: all flags in this byte stay high until cleared by por or until the status byte is read. bit name por function 7 (msb) maskall 0 masks all alert interrupts when high. 6 run/stop 0 standby mode control bit. if high, the device immediately stops converting and enters standby mode. if low, the device converts. 5 mask4* 0 masks remote dx4 interrupts when high. 4 mask3* 0 masks remote dx3 interrupts when high. 3 mask2 0 masks remote dx2 interrupts when high. 2 mask1 0 masks remote dx1 interrupts when high. 0 ibias1 0 m ed i um /l ow - b i as contr ol b i t. h i g h = l ow b i as, l ow = m ed i um b i as. ibias 0 m ust b e l ow . 1 ibias0 0 high-bias control bit. high bias on dxp_ when high. overrides ibias1. bit name function 7 (msb) busy a high indicates that the adc is busy converting. 6 lhigh ? a high indicates that the local high-temperature alarm has activated. 5 llow ? a high indicates that the local low-temperature alarm has activated. 4 open ? a high indicates one of the remote-diode continuity (open-circuit) faults. 3 alarm ? a high indicates one of the remote-diode channels has over/undertemperature alarm. 2 n/a n/a 1 n/a n/a 0 n/a n/a bit name function 7 (msb) rlow1 a high indicates that the dx1 low-temperature alarm has activated. 6 rhigh1 a high indicates that the dx1 high-temperature alarm has activated. 5 rlow2 a high indicates that the dx2 low-temperature alarm has activated. 4 rhigh2 a high indicates that the dx2 high-temperature alarm has activated. 3 rlow3* a high indicates that the dx3 low-temperature alarm has activated. 2 rhigh3* a high indicates that the dx3 high-temperature alarm has activated. 1 rlow4* a high indicates that the dx4 low-temperature alarm has activated. 0 rhigh4* a high indicates that the dx4 high-temperature alarm has activated. *not available for max1805. ? these flags stay high until cleared by por, or until the status byte register is read. *not available for max1805.
max1668/max1805/MAX1989 ? multichannel remote/local temperature sensors ______________________________________________________________________________________ 15 figure 5. smbus write timing diagram figure 4. smbus read timing diagram smbclk a = start condition b = msb of address clocked into slave c = lsb of address clocked into slave d = r/w bit clocked into slave ab cd e fg h i j smbdata t su:sta t hd:sta t low t high t su:dat t su:sto t buf k e = slave pulls smbdata line low f = acknowledge bit clocked into master g = msb of data clocked into master h = lsb of data clocked into master i = acknowledge clock pulse j = stop condition k = new start condition smbclk ab cd e fg h i j k smbdata t su:sta t hd:sta t low t high t su:dat t hd:dat t su:sto t buf a = start condition b = msb of address clocked into slave c = lsb of address clocked into slave d = r/w bit clocked into slave e = slave pulls smbdata line low l m f = acknowledge bit clocked into master g = msb of data clocked into slave h = lsb of data clocked into slave i = slave pulls smbdata line low j = acknowledge clocked into master k = acknowledge clock pulse l = stop condition, data executed by slave m = new start condition table 8. slave address decoding (add0 and add1) note: high-z means that the pin is left unconnected and floating. 0011 001 high-z gnd 0011 000 address 0101 001 gnd high-z 0011 010 v cc gnd 0101 011 v cc high-z 0101 010 1001 101 high-z v cc 1001 100 gnd gnd gnd v cc high-z high-z 1001 110 v cc v cc add0 add1
max1668/max1805/MAX1989 ? multichannel remote/local temperature sensors 16 ______________________________________________________________________________________ qsop.eps package information (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation go to www.maxim-ic.com/packages .)
max1668/max1805/MAX1989 ? multichannel remote/local temperature sensors 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. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ____________________ 17 ? 2003 maxim integrated products printed usa is a registered trademark of maxim integrated products. tssop4.40mm.eps package information (continued) (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation go to www.maxim-ic.com/packages .)

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