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general description the MAX1253/max1254 are stand-alone, 10-channel (8 external, 2 internal) 12-bit system monitor adcs with internal reference. a programmable single-ended/dif- ferential mux accepts voltage and remote-diode tem- perature-sensor inputs. these devices independently monitor the input channels without microprocessor interaction and generate an interrupt when any variable exceeds user-defined limits. the MAX1253/max1254 configure both high and low limits, as well as the num- ber of fault cycles allowed, before generating an inter- rupt. these adcs can also perform recursive data averaging for noise reduction. programmable wait inter- vals between conversion sequences allow the selection of the sample rate. at the maximum sampling rate of 94ksps (auto mode, single channel enabled), the MAX1253 consumes only 5mw (1.7ma at 3v). autoshutdown tm reduces supply current to 190? at 2ksps and to less than 8? at 50sps. stand-alone operation, combined with ease of use in a small package (16-pin tssop), makes the MAX1253/ max1254 ideal for multichannel system-monitoring applications. low power consumption also makes these devices a good fit for hand-held and battery-pow- ered applications. applications system supervision remote telecom networks server farms remote data loggers features monitor 10 signals without processor intervention eight external channels programmable as temperature or voltage monitors intelligent circuitry for reliable autonomous measurement programmable digital averaging filter programmable fault counter precision measurements 12-bit resolution ? lsb inl, ? lsb dnl ?.75? temperature accuracy (typ) flexible automatic channel scan sequencer with programmable intervals programmable inputs: single ended/differential, voltage/temperature programmable wait state internal 2.5v/4.096v reference (MAX1253/max1254) remote temperature sensing up to 10m (differential mode) single 3v or 5v supply operation small 16-pin tssop package MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor ________________________________________________________________ maxim integrated products 1 selector guide 19-2838; rev 0; 4/03 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. * future product?ontact factory for availability. * future product?ontact factory for availability. typical application circuit appears at end of data sheet. autoshutdown is a trademark of maxim integrated products, inc. part inl (lsb) temp error ( c) supply voltage (v) MAX1253aeue* ? ?.0 2.7 to 3.6 MAX1253beue ? ?.0 2.7 to 3.6 max1254aeue* ? ?.0 4.5 to 5.5 max1254beue ? ?.5 4.5 to 5.5 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 ain0 sclk cs din v dd gnd dout int ref top view MAX1253 max1254 16 tssop ain1 ain2 ain5 ain3 ain4 ain6 ain7 pin configuration ordering information part temp range pin-package MAX1253 aeue* -40? to +85? 16 tssop MAX1253beue -40? to +85? 16 tssop max1254 aeue* -40? to +85? 16 tssop max1254beue -40? to +85? 16 tssop
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor 2 _______________________________________________________________________________________ absolute maximum ratings stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. v dd to gnd .............................................................-0.3v to +6v analog inputs to gnd (ain0?in7, ref) ... -0.3v to (v dd + 0.3v) digital inputs to gnd (din, sclk, cs ) .... -0.3v to (v dd + 0.3v) digital outputs to gnd (dout, int) ........ -0.3v to (v dd + 0.3v) digital outputs sink current ............................................. 25ma maximum current into any pin .......................................... 50ma continuous power dissipation (t a = +70?) 16-pin tssop (derate 8.7mw/? above +70?) .........696mw operating temperature range ...........................-40? to +85? junction temperature ......................................................+150? storage temperature range .............................-65? to +150? lead temperature (soldering, 10s) .................................+300? parameter symbol conditions min typ max units dc accuracy resolution res 12 bits grade a 1.0 integral nonlinearity (note 1) inl grade b 1.0 lsb differential nonlinearity dnl no missing codes overtemperature 1.0 lsb offset error 4.0 lsb external reference 4.0 lsb gain error (note 2) internal reference 2.0 %fsr offset error tempco 5p p m / c external reference 2 gain and temperature coefficient internal reference 30 p p m / c c hannel - to- c hannel offset m atchi ng 0.1 lsb v dd m oni tor accur acy internal reference 2.5 % dynamic accuracy (10khz sine-wave input, 2.5v p-p (MAX1253), 4.096v p-p (max1254), 64ksps, f sclk = 10mhz, bipolar input mode) signal-to-noise plus distortion sinad 70 db total harmonic distortion thd up to the 5th harmonic -76 db spurious-free dynamic range sfdr 72 db full-power bandwidth -3db point 1 mhz full linear bandwidth s / (n + d) > 68db 100 khz conversion rate voltage measurement, all ref modes 10.6 11.7 temp-sensor ref modes 01, 10 46 50.7 conversion time (note 3) t conv temp-sensor ref mode 00 73 80 s single-channel throughput manual trigger, voltage measurement 70 ksps power-up time t pu internal reference (note 4) 40 45 s analog input (ain0 ain7) u ni p ol ar , si ng l e- end ed , or d i ffer enti al i np uts 0 +v ref input voltage range (note 5) bipolar, differential inputs -v ref / 2 +v ref / 2 v common-mode range differentially configured inputs 0 v dd v common-mode rejection d i ffer enti all y confi g ur ed i np uts, v c m = 0 to v d d -90 db electrical characteristics (v dd = +2.7v to +3.6v (MAX1253), v dd = +4.5v to +5.5v (max1254), v ref = +2.5v (MAX1253), v ref = +4.096v (max1254), f sclk = 10mhz (50% duty cycle), t a = t min to t max , unless otherwise noted. typical values are at t a = +25 c.)
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor _______________________________________________________________________________________ 3 parameter symbol conditions min typ max units input leakage current on-/off-leakage, v in = 0 or v dd 1 a input capacitance (note 6) 18 pf temperature measurements t a = -20 c to +85 c 0.5 1.0 t a = -40 c to +85 c 0.75 1.5 grade a MAX1253 max1254 t a = +25 c 0.3 t a = -40 c to +85 c 1.2 2.5 grade b MAX1253 t a = +25 c 0.7 t a = -40 c to +85 c 1.2 3.0 internal sensor measurement error (note 7) grade b max1254 t a = +25 c 0.7 c t a = -40 c to +85 c2 differential t a = +25 c1 t a = -40 c to +85 c5 external sensor measurement error (note 8) single ended t a = +25 c2 c differentially configured inputs and internal sensor 0.3 temperature measurement noise single-ended configured, external sensor 0.1 c temperature resolution 0.125 c/lsb low 4 external sensor bias current high 66 a differentially configured inputs and internal sensor 0.3 power-supply rejection psr single-ended configured, external sensor 0.1 c/v internal reference MAX1253 2.456 2.500 2.544 ref output voltage v ref max1254 4.024 4.096 4.168 v grade a 8 ref temperature coefficient tc ref grade b 30 p p m / c ref output resistance 7k ? MAX1253 200 ref output noise max1254 160 v rms MAX1253 -70 -50 ref power-supply rejection ratio psrr max1254 -70 -50 db external reference ref input voltage range v ref 1.0 v dd + 0.05 v v ref = +2.5v; f sample = 94ksps 15 40 ref input current i ref in power-down 1 a electrical characteristics (continued) (v dd = +2.7v to +3.6v (MAX1253), v dd = +4.5v to +5.5v (max1254), v ref = +2.5v (MAX1253), v ref = +4.096v (max1254), f sclk = 10mhz (50% duty cycle), t a = t min to t max , unless otherwise noted. typical values are at t a = +25 c.)
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor 4 _______________________________________________________________________________________ electrical characteristics (continued) (v dd = +2.7v to +3.6v (MAX1253), v dd = +4.5v to +5.5v (max1254), v ref = +2.5v (MAX1253), v ref = +4.096v (max1254), f sclk = 10mhz (50% duty cycle), t a = t min to t max , unless otherwise noted. typical values are at t a = +25 c.) parameter symbol conditions min typ max units digital inputs (sclk, din, cs ) input voltage low v il v dd x 0.3 v input voltage high v ih v dd x 0.7 v input hysteresis v hyst 200 mv input leakage current i in v in = 0 or v dd 10 a input capacitance c in 2pf digital outputs (int, dout) i sink = 8ma, dout 0.5 output voltage low v ol i sink = 2ma, int 0.5 v i source = 8ma, dout v dd - 0.5 output voltage high v oh i source = 2ma, int v dd - 0.5 v tri-state leakage current i l cs = v dd 10 a tri-state output capacitance c out cs = v dd 5pf power requirements MAX1253 2.7 3.6 positive supply voltage v dd max1254 4.5 5.5 v MAX1253 internal reference (note 9) 3.3 MAX1253 internal reference (note 10) 2.9 MAX1253 external reference (note 10) 2.2 max1254 internal reference (note 9) 5.0 max1254 internal reference (note 10) 4.0 max1254 external reference (note 10) 3.0 ma supply current i dd both internal reference, mode 01 (note 11) 8 a MAX1253 480 full power-down supply current i shdn full power-down state max1254 860 na power-supply rejection ratio psrr analog inputs at full scale (note 12) 0.4 1.6 mv/v
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor _______________________________________________________________________________________ 5 note 1: relative accuracy is the deviation of the analog value at any code from its theoretical value after the gain and offset errors have been calibrated. note 2: offset nulled. note 3: in reference mode 00, the reference system powers up for each temperature measurement. in reference mode 01, the ref- erence system powers up once per sequence of channels scanned. if a sample wait <80s is programmed, the reference system is on all the time. in reference mode 10, the reference system is on all the time (see table 7). note 4: no external capacitor on ref. note 5: the operational input voltage range for each individual input of a differentially configured pair (ain0 ain7) is from gnd to v dd . the operational input voltage difference is from -v ref /2 to +v ref /2. note 6: see figure 3 and the sampling error vs. input source impedance graph in the typical operating characteristics section. note 7: grade a tested at +10 c and +55 c. -20 c to +85 c and -40 c to +85 c specifications guaranteed by design. grade b tested at +25 c. t min to t max specification guaranteed by design. note 8: external temperature measurement mode using an mmbt3904 (diodes inc.) as a sensor. external temperature sensing from -40 c to +85 c; MAX1253/max1254 held at +25 c. note 9: performing eight single-ended external channels temperature measurements, an internal temperature measurement, and an internal v dd measurement with no sample wait results in a conversion rate of 2ksps per channel. note 10: performing eight single-ended voltage measurements, an internal temperature measurement, and an internal v dd measure- ment with no sample wait results in a conversion rate of 7ksps per channel. note 11: performing eight single-ended voltage measurements, an internal temperature measurement, and an internal v dd measure- ment with maximum sample wait results in a conversion rate of 3ksps per channel. note 12: defined as the shift in the code boundary as a result of supply voltage change. v dd = min to max; full-scale input, mea- sured using external reference. timing characteristics (v dd = +2.7v to +3.6v (MAX1253), v dd = +4.5v to +5.5v (max1254), t a = t min to t max , unless otherwise noted.) (figures 1, 2, and 4) parameter symbol conditions min typ max units sclk clock period t cp 100 0.5 ns sclk pulse width high time t ch 45 ns sclk pulse width low time t cl 45 ns din to sclk setup time t ds 25 ns din to sclk hold time t dh 0ns cs fall to sclk rise setup t css 25 ns sclk rise to cs rise hold t csh 50 ns sclk fall to dout valid t dov c l = 30pf 50 ns cs rise to dout disable t dod c l = 30pf 40 ns cs fall to dout enable t doe c l = 30pf 40 ns cs pulse width high t csw 40 ns
supply current vs. sample rate MAX1253/54 toc07 sample rate (khz) supply current (ma) 10 1 0.1 0.01 0.01 0.1 1 10 0.001 0.001 100 internal reference (mode 01) max1254 9 temperature channels and 1 voltage channel 9 voltage channels and 1 temperature channel 1 voltage channel (v dd /2) supply current vs. supply voltage MAX1253/54 toc08 supply voltage (v) supply current (ma) 5.1 4.7 3.1 3.5 3.9 4.3 1.4 1.8 2.2 2.6 3.0 3.4 3.8 4.2 1.0 2.7 5.5 external reference (mode 00) 9 voltage channels and 1 temperature channel 1 voltage channel (v dd /2) 9 temperature channels and 1 voltage channel reference voltage vs. temperature MAX1253/54 toc05 temperature ( c) reference voltage (v) 60 40 20 0 -20 2.492 2.494 2.496 2.498 2.500 2.502 2.504 2.506 2.508 2.510 2.490 -40 80 grade a grade b MAX1253 reference voltage vs. temperature MAX1253/54 toc05b temperature ( c) reference voltage (v) 60 40 20 0 -20 4.0725 4.0750 4.0775 4.0800 4.0825 4.0850 4.0875 4.0900 4.0700 -40 80 grade a max1254 grade b supply current vs. sample rate MAX1253/54 toc06 sample rate (khz) supply current (ma) 10 1 0.1 0.01 0.01 0.1 1 10 0.001 0.001 100 internal reference (mode 01) MAX1253 9 temperature channels and 1 voltage channel (v dd /2) 9 voltage channels and 1 temperature channel 1 voltage channel (v dd /2) internal reference voltage vs. supply voltage MAX1253/54 toc04 supply voltage (v) internal reference voltage (v) 5.4 5.3 5.1 5.2 4.7 4.8 4.9 5.0 4.6 4.077 4.079 4.081 4.083 4.085 4.075 4.5 5.5 max1254 MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor 6 _______________________________________________________________________________________ typical operating characteristics (v dd = +3v, v ref = 2.5v (MAX1253); v dd = 5v, v ref = 4.096v (max1254); f sclk = 10mhz, c ref = 0.1f, t a = +25 c, unless oth- erwise noted.) integral nonlinearity vs. digital output code MAX1253/54 toc01 output code inl (lsb) 3072 2048 1024 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1.0 -1.0 0 4096 differential nonlinearity vs. digital output code MAX1253/54 toc02 output code dnl (lsb) 3072 2048 1024 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1.0 -1.0 0 4096 internal reference voltage vs. supply voltage MAX1253/54 toc03 supply voltage (v) internal reference voltage (v) 3.5 3.4 3.2 3.3 2.9 3.0 3.1 2.8 2.501 2.502 2.503 2.504 2.505 2.506 2.507 2.508 2.509 2.510 2.500 2.7 3.6 MAX1253
gain error vs. temperature MAX1253/54 toc15 temperature ( c) gain error (lsb) 80 65 50 35 20 5 -10 -25 0.10 0 0.20 0.40 0.30 0.60 0.50 0.70 0.90 0.80 1.00 -0.10 -40 unipolar differential configuration external reference mode bipolar differential configuration external reference mode unipolar single-ended configuration external reference mode offset error vs. temperature MAX1253/54 toc16 temperature ( c) offset error (lsb) 80 65 50 35 20 5 -10 -25 -0.80 -0.60 -0.40 -0.20 0 0.20 0.40 -1.00 -40 unipolar differential configuration external reference mode bipolar differential configuration external reference mode unipolar single-ended configuration external reference mode internal temperature sensor temperature error MAX1253/54 toc17 temperature ( c) error ( c) 60 40 20 0 -20 -0.80 -0.60 -0.40 -0.20 0 0.20 0.40 0.60 0.80 1.00 -1.00 -40 80 MAX1253/max1254 grade a internal sensor grade b internal sensor MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor _______________________________________________________________________________________ 7 typical operating characteristics (continued) (v dd = +3v, v ref = 2.5v (MAX1253); v dd = 5v, v ref = 4.096v (max1254); f sclk = 10mhz, c ref = 0.1f, t a = +25 c, unless oth- erwise noted.) supply current vs. supply voltage MAX1253/54 toc09 supply voltage (v) supply current (ma) 5.1 4.7 3.1 3.5 3.9 4.3 1.9 2.3 2.7 3.1 3.5 3.9 4.3 1.5 2.7 5.5 internal reference (mode 01) 9 temperature channels and voltage channel (v dd /2) 9 voltage channels and 1 temperature channel 1 voltage channel (v dd /2) supply current vs. temperature MAX1253/54 toc10 temperature ( c) supply current (ma) 80 65 35 50 -10 5 20 -25 1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 1.6 -40 9 temperature channels and 1 voltage channel (v dd /2) 9 voltage channels and 1 temperature channel 1 voltage channel (v dd /2) internal reference (mode 01) MAX1253 supply current vs. temperature MAX1253/54 toc11 temperature ( c) supply current (ma) 80 65 35 50 -10 5 20 -25 2.5 3.0 4.0 3.5 4.5 5.0 2.0 -40 9 temperature channels and 1 voltage channel (v dd /2) 9 voltage channels and 1 temperature channel 1 voltage channel (v dd /2) internal reference (mode 01) max1254 shutdown supply current vs. supply voltage MAX1253/54 toc12 supply voltage (v) shutdown supply current (na) 5.1 4.7 4.3 3.9 3.5 3.1 200 300 400 500 600 700 100 2.7 5.5 MAX1253 max1254 shutdown supply current vs. temperature MAX1253/54 toc13 temperature ( c) shutdown supply current (na) 65 50 35 20 5 -10 -25 100 200 300 400 500 600 700 0 -40 80 max1254 v dd = 5v MAX1253 v dd = 3v gain and offset error vs. supply voltage MAX1253/54 toc14 supply voltage (v) gain and offset error (lsb) 5.1 4.7 3.9 4.3 3.5 3.1 -0.80 -0.60 -0.40 -0.20 0 0.20 0.40 0.60 0.80 1.00 -1.00 2.7 5.5 single ended MAX1253 max1254 offset error gain error
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor 8 _______________________________________________________________________________________ external temperature sensor temperature error MAX1253/54 toc18 temperature ( c) error ( c) 60 40 20 0 -20 -1.6 -1.2 -0.8 -0.4 0 0.4 0.8 1.2 1.6 2.0 -2.0 -40 80 MAX1253/max1254 external sensor, differential input external sensor, single-ended input temperature error vs. interconnect capacitance (external sensor) MAX1253/54 toc19 interconnect capacitance (pf) temperature ( c) -5 -4 -3 -2 -1 0 1 -6 1 10 100 1000 external diode differential temperature measurement mode sampling error vs. input source impedance MAX1253/54 toc20 source impedance ( ? ) sampling error (lsb) 1000 100 -4 -3 -2 -1 0 1 -5 10 10,000 turn on thermal transient, continuous conversion v dd = 3.0v MAX1253/54 toc21 time (s) temperature shift ( c) 25 20 15 10 5 0 0.125 0.250 0.375 0.500 0.625 -0.125 030 in a tssop socket solder on a 2in ? 2in pwb in an oil bath external bjt typical operating characteristics (continued) (v dd = +3v, v ref = 2.5v (MAX1253); v dd = 5v, v ref = 4.096v (max1254); f sclk = 10mhz, c ref = 0.1f, t a = +25 c, unless oth- erwise noted.)
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor _______________________________________________________________________________________ 9 pin description pin name function 1 ain0 analog voltage input/temperature input channel 0 or positive differential input relative to ain1 2 ain1 analog voltage input/temperature input channel 1 or negative differential input relative to ain0 3 ain2 analog voltage input/temperature input channel 2 or positive differential input relative to ain3 4 ain3 analog voltage input/temperature input channel 3 or negative differential input relative to ain2 5 ain4 analog voltage input/temperature input channel 4 or positive differential input relative to ain5 6 ain5 analog voltage input/temperature input channel 5 or negative differential input relative to ain4 7 ain6 analog voltage input/temperature input channel 6 or positive differential input relative to ain7 8 ain7 analog voltage input/temperature input channel 7 or negative differential input relative to ain6 9 ref positive reference input in external mode. bypass ref with a 0.1f capacitor to gnd when in external mode. when using the internal reference, ref must be left open. 10 int interrupt output. push-pull or open drain with selectable polarity. see table 9 and the int interrupt output section. 11 dout serial data output. dout transitions on the falling edge of sclk. high impedance when cs is at logic high. 12 gnd ground 13 v dd positive power supply. bypass with a 0.1f capacitor to gnd. 14 din serial data input. din data is latched into the serial interface on the rising edge of the sclk. 15 sclk serial clock input. clocks data in and out of the serial interface (duty cycle must be 40% to 60%). 16 cs active-low chip-select input. when cs is low, the serial interface is enabled. when cs is high, dout is high impedance, and the serial interface resets. accumulator internal temp upper threshold lower threshold channel configuration accumulator v dd /2 upper threshold lower threshold channel configuration accumulator ain0 upper threshold lower threshold channel configuration accumulator ain1 upper threshold lower threshold channel configuration accumulator ain2 upper threshold lower threshold channel configuration accumulator ain3 upper threshold lower threshold channel configuration accumulator ain4 upper threshold lower threshold channel configuration accumulator ain5 upper threshold lower threshold channel configuration accumulator ain6 upper threshold lower threshold channel configuration accumulator ain7 upper threshold lower threshold channel configuration ain7 ain6 ain5 ain4 ain3 ain2 ain1 v dd mux temp sensor reference 12-bit adc with t/h scan and conversion control por power- good input channel register input configuration register step-up register alarm register averaging digital comparator serial interface ref dout din sclk int cs MAX1253 max1254 block diagram
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor 10 ______________________________________________________________________________________ gnd a) v ol to v oh c load = 100pf 100na dout gnd v dd b) high-z to v ol and v oh to v ol c load = 100pf 100na dout figure 1. load circuits for dout enable time and sclk to dout delay time gnd a) v oh to high-z c load = 100pf 100na dout gnd v dd b) v ol to high-z c load = 100pf 100na dout figure 2. load circuit for dout disable time detailed description the MAX1253/max1254 are precision-monitoring inte- grated circuit systems specifically intended for stand- alone operation. they can monitor diverse types of inputs, such as those from temperature sensors and voltage signals from pressure, vibration, and accelera- tion sensors, and digitize these input signals. the digi- tal values are then compared to preprogrammed thresholds and, if the thresholds are exceeded, the processor is alerted by an interrupt signal. no interac- tion by the cpu or microcontroller (c) is required until one of the programmed limits is exceeded (figures 3 and 4). voltages on all the inputs are converted to 12-bit values sequentially and stored in the current data registers. note that eight of these inputs are external and two are internal. one of the internal inputs monitors the v dd voltage supply, while the other monitors the internal ic temperature. ain0 to ain7 can be configured as either single ended (default) or differential. in addition, these inputs can be configured for single-ended or differen- tial temperature measurements. in the temperature configuration, the device provides the proper bias nec- essary to measure temperature with a diode-connected transistor sensor. the user enables which inputs are measured (both external and internal) and sets the delay between each sequence of measurements dur- ing the initial setup of the device. the values stored in the current data registers are com- pared to the user-preprogrammed values in the thresh- old registers (upper and lower thresholds) and, if exceeded, activate the interrupt output and generate an alarm condition. if desired, the device can be pro- grammed to average the results of many measurements before comparing to the threshold value. this reduces the sensitivity to external noise in the measured signal. in addition, the user can set the number of times the threshold is exceeded (fault cycles) before generating an interrupt. this feature reduces falsely triggered alarms caused by undesired, random spurious impulses. when the fault cycle criterion is exceeded, an alarm condition is created. the device writes the fault condi- tion into the alarm register to indicate the alarmed input channel. converter operation the MAX1253/max1254 adcs use a fully differential successive-approximation register (sar) conversion technique and an on-chip track-and-hold (t/h) block to convert temperature and voltage signals into a 12-bit digital result. both single-ended and differential config- urations are supported with a unipolar signal range for single-ended mode and bipolar or unipolar ranges for differential mode. figure 5 shows the equivalent input circuit for the MAX1253/max1254. configure the input channels according to tables 5 and 6 (see the input configuration register section). in single-ended mode, the positive input (in+) is con- nected to the selected input channel and the negative input (in-) is connected to gnd. in differential mode, in+ and in- are selected from the following pairs: ain0/ain1, ain2/ain3, ain4/ain5, and ain6/ain7. once initiated, voltage conversions require 10.6s (typ) to complete.
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor ______________________________________________________________________________________ 11 during the acquisition interval, in+ and in- charge both a positive (choldp) and a negative (choldn) sam- pling capacitor. after completing the acquisition inter- val, the t/h switches open, storing an accurate sample of the differential voltage between in+ and in-. this charge is then transferred to the adc and converted. finally, the conversion result is transferred to the cur- rent data register. temperature conversions require 46s (typ) and mea- sure the difference between two sequential voltage measurements (see the temperature measurement section for a detailed description). fully differential track/hold (t/h) the t/h acquisition interval begins with the rising edge of cs (for manually triggered conversions) and is inter- nally timed to 1.5s (typ). the accuracy of the input sig- nal sample is a function of the input signal s source impedance and the t/h s capacitance. in order to achieve adequate settling of the t/h, limit the signal source impedance to a maximum of 1k ? . input bandwidth the adc s input tracking circuitry has a 1mhz small- signal bandwidth. to avoid high-frequency signals aliasing into the frequency band of interest, anti-alias prefiltering of the input signals is recommended. analog input protection internal protection diodes, which clamp the analog inputs to v dd and gnd, allow the channel input pins to swing from (gnd - 0.3v) to (v dd + 0.3v) without dam- age. however, for accurate conversions near full scale, the inputs must not exceed v dd by more than 50mv or be lower than gnd by 50mv. if the analog input range must exceed 50mv beyond the supplies, limit the input current. single ended/differential the MAX1253/max1254 use a fully differential adc for all conversions. through the input configuration regis- ter, the analog inputs can be configured for either dif- ferential or single-ended conversions. when sampling signal sources close to the MAX1253/max1254, single- ended conversion is generally sufficient. single-ended conversions use only one analog input per signal source, internally referenced to gnd. mux ain0 v dd ain1 ain2 ain3 ain4 ain5 ain6 ain7 temp sense 12-bit adc with t/h digital comparator input registers current data upper threshold lower threshold # fault cycles average configuration/ status registers scan and conversion control serial interface din int dout sclk cs figure 3. simplified alarm block diagram of the MAX1253/max1254
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor 12 ______________________________________________________________________________________ is channel enabled? sample channel average converted channel data is avg data > upper? same fault as previous? reset fault counter increment fault counter is avg data < lower? increment channel counter is fault cnt > fault reg? set alarm register no yes convert channel yes no yes no no no yes yes figure 4. alarm flowchart
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor ______________________________________________________________________________________ 13 in differential mode, the t/h samples the difference between two analog inputs, eliminating common-mode dc offsets and noise. see the input configuration register section and tables 5 and 6 for more details on configuring the analog inputs. unipolar/bipolar when performing differential conversions, the input configuration register (tables 5 and 6) also selects between unipolar and bipolar operation. unipolar mode sets the differential input range from 0 to v ref. a nega- tive differential analog input in unipolar mode causes the digital output code to be zero. selecting bipolar mode sets the differential input range to v ref /2. the digital output code is straight binary in unipolar mode and two s complement in bipolar mode (see the transfer function section). in single-ended mode, the MAX1253/max1254 always operate in unipolar mode. the analog inputs are inter- nally referenced to gnd with a full-scale input range from 0 to v ref. digital interface the MAX1253/max1254 digital interface consists of five signals: cs , sclk, din, dout, and int. cs , sclk, din, and dout comprise an spi -compatible serial interface (see the serial digital interface section) . int is an independent output that provides an indica- tion that an alarm has occurred in the system (see the int interrupt output section). serial digital interface the MAX1253/max1254 feature a serial interface com- patible with spi, qspi , and microwire devices. for spi/qspi, ensure that the cpu serial interface runs in master mode so it generates the serial clock signal. select a serial clock frequency of 10mhz or less, and set clock polarity (cpol) and phase (cpha) in the p control registers to the same value, one or zero. the MAX1253/max1254 support operation with sclk idling high or low, and thus operate with cpol = cpha = 0 or cpol = cpha = 1. t t tt h hh v az v dd adc choldp chold choldn 8-to-1 differential mux temp differential input equivalent input circuit t t h h v az v dd adc 8-to-1 differential mux temp single-ended input equivalent input circuit figure 5. single-ended/differential input equivalent input circuit spi and qspi are trademarks of motorola, inc. microwire is a trademark of national semiconductor corp.
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor 14 ______________________________________________________________________________________ clock pulses on sclk shift data into din on the rising edge of the sclk and out of dout on the falling edge of sclk. data transfers require a logic low on cs . a high-to-low transition of cs marks the beginning of a data transfer. a logic high on cs at any time resets the serial interface. see figure 6 and the timing characteristics table for detailed serial-interface timing information. input data format serial communications always begin with an 8-bit com- mand word, serially loaded from din. a high-to-low transition on cs initiates the data input operation. the command word and the subsequent data bytes (for write operations) are clocked from din into the MAX1253/max1254 on the rising edges of sclk. the first rising edge on sclk, after cs goes low, clocks in the msb of the command word (see the command word section). the next seven rising edges on sclk complete the loading of the command word into the internal command register. after the 8-bit command word is entered, transfer 0 to 20 bytes of data, depend- ing on the command. table 2 shows the number of data bytes for each command. output data format output data from the MAX1253/max1254 is clocked onto dout on the falling edge of sclk. single-ended and unipolar differential measurements are output in straight binary msb first, with two 8-bytes-per-conver- sion result, and the last 4 bits padded with zeros. for temperature and bipolar differential voltage measure- ments, the output is two s complement binary in the same 2-byte format. the msb of the output data from a read command transitions at dout after the falling edge of the 8th sclk clock pulse following the cs high-to-low transition. table 2 shows the number of bytes to be read from dout for a given read com- mand. command word the command word (table 1) controls all serial com- munications and configuration of the MAX1253/ max1254, providing access to the 44 on-chip registers. the first 4 msbs of the command word specify the command (table 2), while the last 4 bits provide address information. the first rising edge on sclk, after cs goes low, trans- fers the command word msb into din. the next seven rising edges on sclk shift the remaining 7 bits into the internal command register (see the serial digital interface section). high-z high-z t css t doe t ds t dh t ch t cl t cp t dov t dod t csh t csw sclk din dout cs figure 6. detailed serial interface timing diagram table 1. command word b7 (msb) b6 b5 b4 b3 b2 b1 b0 (lsb) command b3 command b2 command b1 command b0 address b3 address b2 address b1 address b0
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor ______________________________________________________________________________________ 15 manually triggered conversion (command code = 0000) before beginning a manual conversion, ensure the scan mode bit in the setup register is zero, because a logic 1 disables manual conversions. the address bits in a manually triggered conversion command select the input channel for conversion (see table 3). when performing a differential conversion, use the even chan- nel address (ain0, ain2, ain4, ain6); the command is ignored if odd channel addresses (ain1, ain3, ain5, ain7) are used for a differential conversion. after issuing a manually triggered conversion com- mand, bring cs high to begin the conversion. to obtain a correct conversion result, cs must remain high for a period longer than the reference power-up time (if in power-down mode) plus the conversion time for the selected channel configured conversion type (voltage or temperature). the conversion s result can then be read at dout by issuing a read current data register for selected channel command, addressing the con- verted channel. see table 3 for channel addresses. table 2. command description data bytes after command word command word bytes to din bytes from dout command description 0000#### 0 0 manually trigged conversion 0001xxxx 0 3 read alarm register 0010#### 0 2 read current data register for selected channel 0011#### 0 20 read current data register for all channels 0100#### 0 5 read configuration register for selected channel 0101xxxx 0 5 read global configuration registers 0110xxxx n/a n/a reserved 0111xxxx 0 0 reset 1000#### 0 0 clear alarm/fault for selected channels 1001xxxx 0 0 clear alarm/fault for all channels 1010#### 2 0 write current data register for selected channel 1011xxxx 20 0 write current data registers for all channels 1100#### 5 0 write configuration registers for selected channel 1101xxxx 5 0 write global configuration registers 1110xxxx n/a n/a reserved 1111xxxx n/a n/a reserved #### = channel address code, see table 3. xxxx = these bits are ignored for this command. table 3. channel address address in command input 0000 internal temperature 0001 vdd 0010 ain0 0011 ain1 0100 ain2 0101 ain3 0110 ain4 0111 ain5 1000 ain6 1001 ain7 1010 reserved 1011 reserved 1100 reserved 1101 reserved 1110 reserved 1111 reserved
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor 16 ______________________________________________________________________________________ read alarm register (command code 0001) the read alarm register command, 0001, outputs the current status of the alarm register (see table 11). the address bits in this command are ignored. the alarm register is 24 bits long and outputs in 3 bytes. table 12 illustrates the encoding of the alarm register. after receiving an interrupt, read the alarm register to determine the source of the interrupt (see the alarm register section). read current data register for selected channel (command code 0010) the read current data register for selected channel command, 0010, outputs the data in the current data register of the selected channel. the address bits fol- lowing this command select the input channel to be read (see table 3). the current data register is a 12-bit register. it takes 2 bytes to read its value. see the output data format and current data registers sec- tions for more details. see table 3 for channel address- es. also, see figure 7. read current data register for all channels (command code 0011) the read current data registers for all channels com- mand, 0011, outputs the data in the current data regis- ters of all 10 channels starting with the internal temperature sensor, then the v dd monitor, followed by ain0 to ain7. the address bits following this command are ignored. it takes 20 bytes to read all of the 10 chan- nels current data registers. read configuration register for selected channel (command code 0100) the read configuration register for selected channel command, 0100, outputs the configuration data of the channel selected by the address bits (see table 3). the first register that shifts out is the upper threshold register (2 bytes), followed by the lower threshold regis- ter (2 bytes), ending with the channel configuration reg- ister (1 byte), all msb first. it takes 5 bytes to read all three registers. see the channel registers section for more details. sclk din dout c3 c2 c1 c0 a2 a1 a0 d11 d10 d9 d8 d7 d6 d5 d4 d3 d2 d1 d0 a3 cs figure 7. serial register read timing
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor ______________________________________________________________________________________ 17 read global configuration register (command code 0101) the read global configuration register command, 0101, outputs the global configuration registers. the address bits following this command are ignored. when the MAX1253/max1254 receive a read global configuration register command, they output 5 bytes of data: 2 bytes from the channel enable register, 2 bytes from the input configuration register, and 1 byte from the setup register, all msb first. see the global configuration registers section for more details. reset (command code 0111) the reset command, 0111, resets the device. this command returns the MAX1253/max1254 to their power-on reset state, placing the device into shutdown mode. the address bits in the command are ignored. see the power-up/reset defaults summary section for more details. clear channel alarm for selected channel (command code 1000) the clear channel alarm command, 1000, clears the alarm bits in the alarm register and resets the fault counter for the addressed channel. see the alarm register section for more details. see table 3 for chan- nel addresses. clear alarm register for all channels (command code 1001) the clear alarm register for all channels command, 1001, clears the entire alarm register and resets the fault counters for the internal temp sensor, the v dd monitor, and the ain0 ain7 channels. the address bits in the command are ignored. see the alarm register section for more details. write current data register for selected channel (command code 1010) the write current data register for selected channel command, 1010, writes to the addressed channel s cur- rent data register. this command sets an initial condi- tion when using the averaging filter option (see the averaging section). this command can also be used for testing the thresholds, fault counters, and alarm func- tions (figure 8). see table 3 for channel addresses. write current data register for all channels (command code 1011) the write current data register for all channels com- mand, 1011, writes to the current data registers of all channels sequentially, starting with the internal temper- ature sensor, then the v dd monitor, followed by chan- nels ain0 to ain7. the address bits are ignored. use this command for testing and setting initial conditions when using the averaging filter option (see the averaging section). c3 c2 c1 c0 a2 a1 a0 d11 d10 d9 d8 d7 d6 d5 d4 d3 d2 d1 d0 high-z high-z sclk din dout a3 cs figure 8. serial register write timing
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor 18 ______________________________________________________________________________________ write-selected channel configuration registers (command code 1100) the write-selected channel configuration register com- mand, 1100, writes to the three channel configuration registers for the addressed channel (see table 3). the first register to be written is the upper threshold (2 bytes), followed by the lower threshold (2 bytes), ending with the channel configuration register (1 byte), all msb first. writing to the configuration registers resets the alarm reg- ister bits and the fault counters for the addressed chan- nel. see the channel registers section for more details. write global configuration registers (command code 1101) the write global configuration registers command, 1101, writes to three registers: the channel-enable reg- ister (2 bytes), the input configuration register (2 bytes), and the setup register (1 byte). the command address bits are ignored. see the global configuration registers section for more details. global configuration registers the global configuration registers consist of the chan- nel-enable register, the input configuration register, and the setup register. these registers hold configuration data common to all channels. channel-enable register the channel-enable register (table 4) controls which channels are converted while in automatic scan mode. the register contents are ignored for manual conver- sion commands. each input channel has a correspond- ing bit in the channel-enable register. a logic high enables the corresponding analog input channel for conversion, while a logic low disables it. in differential configuration, the bits for odd channels are ignored. at power-up and after a reset command, the register contents default to 111111111111b (all channels enabled). input configuration register the input configuration register (table 5) stores the configuration code for each channel as a 3-bit per channel-pair code (see table 6), selecting from five input signal configurations: single-ended unipolar volt- age, single-ended temperature, differential unipolar voltage, differential bipolar voltage, and differential temperature. table 5 shows the input configuration reg- ister format, and table 6 shows the 3-bit encoding for channel configuration. at power-up and after a reset command, the register contents defaults to 000000000000b (all inputs single ended). table 4. channel-enable register format b11 (msb) b10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0 (lsb) temp vdd ain0 ain1 ain2 ain3 ain4 ain5 ain6 ain7 res res table 5. input configuration register format b11 (msb) b10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0 (lsb) ain0 and ain1 configuration ain2 and ain3 configuration ain4 and ain5 configuration ain6 and ain7 configuration table 6. channel configuration coding (3 bits/channel pair) code ain0, ain2, ain4, ain6 configuration ain1, ain3, ain5, ain7 configuration 000 single-ended input (power-up state) single-ended input (power-up state) 001 single-ended input single-ended, external temperature sensor input 010 single-ended, external temperature sensor input single-ended input 011 single-ended, external temperature sensor input single-ended, external temperature sensor input 100 differential unipolar encoded, positive input differential unipolar encoded, negative input 101 differential bipolar encoded, positive input differential bipolar encoded, negative input 110 differential external temperature sensor, positive input differential external temperature sensor, negative input 111 reserved reserved
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor ______________________________________________________________________________________ 19 setup register the 8-bit setup register (table 7) holds configuration data common to all input channels. at power-up and after a reset command, this register defaults to 00000000b. setup register: sample wait bits (b7, b6, b5) these 3 bits in the setup register (table 8) set the wait time between conversion scans. the following are examples of how the MAX1253/max1254 begin a sam- ple sequence (see the setup register: reference selection bits (b1, b0) section). operating in reference mode 00 (external reference for voltage conversions, internal reference for temperature conversions): 1) convert the first-enabled channel. if this channel is a temperature measurement, power up the internal ref- erence (this takes 20s for each enabled tempera- ture measurement in reference mode 00). 2) sequence to the next-enabled channel until all chan- nels have been converted. 3) wait the sample wait period. 4) repeat the procedure. operating in reference mode 01 (internal reference for all conversions, can be powered down between scans): 1) power up the internal reference, if powered down (this takes 40s). 2) convert the first-enabled channel, starting with the internal temperature sensor, if enabled. 3) sequence to the next-enabled channel until all enabled channels have been converted. 4) wait the sample wait time, and enter internal refer- ence power-down mode if this period is greater than 80s. 5) repeat the above steps. operating in reference mode 10 (internal reference for all conversions, continuously powered up): 1) convert the first-enabled channel. 2) sequence to the next-enabled channel until all enabled channels have been converted. 3) wait the sample wait time. 4) repeat the procedure. use the sample wait feature to reduce supply current when measuring slow-changing analog signals. this power savings occurs when reference mode 00 or 01 is used in combination with wait times longer than 80s. with reference mode 10 or wait times of less than 80s, the internal reference system remains powered up, mini- mizing any power savings. see the computing data throughput section. table 8 shows the b7, b6, b5 wait time encoding. setup register: interrupt control (b4, b3) bits b3 and b4 in the setup register configure int and how it responds to an alarm event (see the alarm register section). table 9 shows the available int options. table 7. setup register format b7 (msb) b6 b5 b4 b3 b2 b1 b0 (lsb) sample wait bits interrupt active interrupt polarity scan mode reference source b1 reference source b2 table 8. wait time encoding b7, b6, b5 wait time (ms) 000 0 001 0.080 010 0.395 011 1.310 100 4.970 101 19.600 110 78.200 111 312.000 table 9. interrupt control bit function bit state int operation 1 driven high or low at all times b4 output driver type 0 high-z when inactive, driven (high or low) when active 1acti ve = hig h, i nacti ve = low or hig h- z b3 output polarity 0acti ve = l ow , inacti ve = hig h or hig h- z
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor 20 ______________________________________________________________________________________ setup register: scan mode bit (b2) the scan mode bit selects between automatic scan- ning and manual conversion mode. when set (b2 = 1), the MAX1253/max1254 enter auto- matic scanning mode and convert every enabled chan- nel starting with the internal temperature sensor, followed by the v dd monitor, then sequencing through ain0 to ain7. after converting all the enabled channels, the MAX1253/max1254 enter a wait state set by the sam- ple wait bits in the setup register. after completing the sample wait time, the scan cycle repeats. when b2 = 0, the MAX1253/max1254 are in manual mode and convert only the selected channel after receiving a manually triggered conversion command (see the manually triggered conversion (command code 0000) section). whether in automatic scanning mode or manual mode, a read current data register for selected channel command outputs the last-com- pleted conversion result for the addressed channel at dout. setup register: reference selection bits (b1, b0) the MAX1253/max1254 can be used with an internal or external reference. select between internal and external reference modes through bits b1 and b0 of the setup register (see table 10). alarm register the alarm register (table 11) holds the current alarm sta- tus for all of the monitored signals. this 24-bit register can only be read and cleared. the alarm register has 2 bits for each external input channel, 2 for the onboard temperature sensor, and 2 for the v dd monitor (see table 12). at power-up, these bits are logic low, indicat- ing no alarms at any input. when any bit in the alarm reg- ister is set, int becomes active and remains active until all alarm bits are cleared. after a fault counter exceeds the set threshold, the alarm register bits for that particular channel are updated to indicate an alarm. to clear the interrupt, reset the active alarm bit with the clear alarm register command, clear channel alarm command, a reset command, or by writing a new configuration to the faulting channel. the alarm register defaults to 000000 hex. table 11 illustrates how the alarm register stores the information on which channel a fault has occurred. the alarm code for each bit pair is shown in table 12. channel registers each channel (internal temperature sensor, v dd moni- tor, and ain0 to ain7) has registers to hold the conver- sion result (current data register) and channel-specific configuration data. the channel-specific configuration registers include: the upper threshold register, the lower threshold register, and the channel configuration register. in differential mode, only the registers for the even channel of the differential input pair are used. the channel-specific configuration registers for the odd channel of a differential channel pair are ignored. table 10. reference selection b1 b0 reference mode 00 voltage measurements use external reference, while temperature measurements use the internal reference. a 20s reference startup delay is added prior to each temperature measurement in this mode. this is the default mode after power-up and after a software reset. 01 all measurements use the internal reference. a 40s reference startup delay is added prior to starting the scanning of enabled channels, allowing the internal reference to stabilize. note: for sample wait times less than 80s, the reference is continuously powered when in automatic scan mode. 10 all measurements use the internal reference. by selecting this mode, the reference is powered up immediately when cs goes high after writing this configuration. once the reference system is powered up, no further delay is added. 1 1 reserved. table 11. alarm register format b23/b22 b21/b20 b19/b18 b17/b16 b15/b14 b13/b12 b11/b10 b9/b8 b7/b6 b5/b4 b3/b2 b1/b0 temp v dd ain0 ain1 ain2 ain3 ain4 ain5 ain6 ain7 res res table 12. alarm register coding (2 bits/channel) code description 00 no alarm (power-up state) 01 input is below lower threshold 10 input is above upper threshold 00 reserved
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor ______________________________________________________________________________________ 21 channel configuration register each channel has a channel configuration register (table 13) defining the number of consecutive faults to be detected before setting the alarm bits and generat- ing an interrupt, as well as controlling the digital averag- ing. at power-up and after a reset command, the register defaults to 00 hex (no averaging, alarm on first fault). fault bits the value stored in the fault bits (b7 b4) in the channel configuration register sets the number of faults that must occur for that channel before generating an inter- rupt. encoding of the fault bits is straight binary with valves 0 to 15. a fault occurs in a channel when the value in its current data register is outside the range defined by the channel s upper and lower threshold registers. for example, if the number of faults set by the fault bits is n, an interrupt is generated when the num- ber of consecutive faults (see note below) reach (n + 1). the fault bits default to 0 hex at power-up. note: consecutive faults are those happening in con- secutive conversion scans for the same channel. if a fault occurs and the next scan finds the input within the normal range defined by the thresholds, the fault counter resets. if the next counter finds the input signal outside the opposite threshold, rather than the previous one, the fault counter also resets. the fault counter increments only when counting consecutive faults exceeding the same threshold (figure 4). averaging the averaging calculated by the data-acquisition algo- rithm of the MAX1253/max1254 improves the input sig- nal-to-noise ratio (snr) by reducing the signal bandwidth digitally. the formula below describes the filter implemented in the MAX1253/max1254: current value = [(n - 1) / n] x past value + [(present value) / n] where n = number of samples indicated in table 14. the averaging bits (b3 b0) in the channel configuration register can set the n factor to any value in table 14. the output of the filter-running algorithm is continuously available in the current data register. the starting value used by the algorithm is the initial state of the current data register. the current data register is reset to mid- scale (800 hex) at power-up or after a reset com- mand, but it can be loaded with a more appropriate initial value to improve the filter settling time. at power-up or after a reset command, the b3 b0 bits of the channel configuration register are set to 0 hex, corresponding to a number of averaged n = 1, no averaging. see table 13 and the write-selected channel configuration registers section for program- ming details. see table 14 for n encoding. as in all digital filters, truncation can be a cause of sig- nificant errors. in the MAX1253/max1254, 24 bits of precision are maintained in the digital averaging func- tion, maintaining a worst-case truncation error of well below an lsb. the worst-case truncation error in the MAX1253/max1254 is given by the following: where n = number of conversions averaged. therefore, the worst truncation error when averaging 256 samples is 0.0623 lsbs. worst case truncation error n lsbs - - = 1 4096 table 13. channel configuration register format b7 (msb) b6 b5 b4 b3 b2 b1 b0 (lsb) fault b3 fault b2 fault b1 fault b0 ave b3 ave b2 ave b1 ave b0 table 14. conversion average encoding code n 0000 1, no averaging 0001 2 0010 4 0011 8 0100 16 0101 32 0110 64 0111 128 1000 256 1001 512 1010 1024 1011 2048 1100 reserved 1101 reserved 1110 reserved 1111 reserved
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor 22 ______________________________________________________________________________________ upper threshold register a conversion result greater than the value stored in the upper threshold register results in a fault, increasing the internal fault counter by one. when the fault count exceeds the value stored in fault bits b7 b4 of the channel configuration register, the channel s alarm bits in the alarm register are set, resulting in an interrupt on int. the upper threshold register data format must be the same as the input channel. when the input channel is configured for single-ended or differential unipolar volt- age measurements, data stored in the upper threshold register is interpreted as straight binary. for input chan- nels configured for temperature measurements or as differential bipolar voltage inputs, the upper threshold register data is interpreted as two s complement. load the register with fff hex to disable upper threshold faults in unipolar mode, and 7ff hex in temperature or bipolar mode. the power-up/reset default is fff hex. see the command word section on how to read/write to the upper threshold registers. lower threshold register conversion results lower than the value stored in the lower threshold register increment the internal fault counter. considerations about channel configuration register fault bits b7 b4, int interrupts, and data for- mat are the same as for the upper threshold register. set the register to 000 hex to disable lower threshold faults in unipolar mode, or to 800 hex in temperature or bipolar mode. the power-up/reset default is 000 hex. see the command word section on how to read/write to the lower threshold registers. current data registers the current data register holds the last conversion result or the digitally averaged result, when enabled (see the averaging section). the current data registers default to 800 hex at power-up/reset and can be read from and written to through the serial interface. see the command word section on how to read/write to the current data registers. int interrupt output int provides an indication that an alarm has occurred in the system. it can be programmed (see table 9) to operate as a push-pull digital output or as an open- drain output (requiring either a pullup or a pulldown resistor) for wired-or interrupt lines. bits b3 and b4 in the setup register configure int and determine its response to an alarm event. when an internal fault counter exceeds the threshold stored in the fault bits (b7 b4) of the corresponding chan- nel configuration register, the alarm bits for that particular channel are updated to indicate an alarm. when any bit in the alarm register is set, the int output becomes active, and stays active until all alarm bits are cleared. see the alarm register section for more information. servicing interrupts at int after detecting an interrupt on int, the c s interrupt routine should first read the alarm register to find the source of the alarm and reset the alarm bits by using any of the methods described in the alarm register section. then it can continue with any other action required by the application to react to the alarm. note: multiple alarm conditions can be present. the int remains active until all alarm conditions have been cleared. performing conversions at power-up or after a reset command, the MAX1253/max1254 default to shutdown mode with all channels enabled, set for single-ended voltage mea- surements, and with the scan mode set to manual. start a conversion by issuing a manually triggered conver- sion command with the address bits of the channel selected (see the manual conversion section for more details) or by setting automatic scan mode. to place the MAX1253/max1254 in automatic scan mode, set scan mode bit b2 in the setup register to logic 1. in automatic scan mode, the MAX1253/max1254 con- vert all enabled channels starting with the internal tem- perature sensor, followed by the v dd monitor, then by ain0 to ain7. as the scan sequence progresses, the analog inputs are converted and the resulting values are stored for each channel into its current data regis- ter. once the scan cycle completes, the MAX1253/ max1254 wait a period determined by the sample wait bits (b7, b6, b5) in the setup register and then repeat the scan cycle. after configuring the MAX1253/max1254 with automat- ic scan mode enabled, the devices do not require any intervention from the system c until an alarm is trig- gered. all conversion and monitoring functions can continue running indefinitely. manual conversion in manual mode (scan mode bit in the setup register set to zero, the default after power-up/reset), the MAX1253/max1254 convert individual channels with the manually triggered conversion command. assuming that, either by power-up/reset defaults or by previous initialization, the channel to be addressed is both enabled and configured for the type of signal to be acquired (voltage/temperature, single ended/differ-
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor ______________________________________________________________________________________ 23 ential, or unipolar/bipolar), carry out the following steps to execute a manual conversion. see figure 9 for man- ual conversion timing: 1) disable autoscan (set up register scan mode bit to zero), if necessary. 2) pull cs low. 3) initiate a conversion by issuing a manually triggered conversion command (0000, followed by the address bits of the channel to be converted). 4) pull cs high to start the conversion. 5) maintain a logic high on cs to allow for reference power-up (if the reference mode requires it) and conversion time. 6) pull cs low. 7) issue a read current data register for selected- channel command (0010, followed by the same address of the channel in the manually triggered conversion command). voltage measurements every voltage measurement (internal v dd or external input channel) requires 10.6s to complete. if the inter- nal reference needs to power up (reference mode = 01), an additional 40s is required every time the MAX1253/max1254 come out of automatic shutdown mode after a sample wait period greater than 80s. monitoring v dd this internal acquisition channel samples and converts the supply voltage, v dd . v dd value can be calculated from the digitized data with the following equation: the reference voltage must be larger than 1/2v dd for the operation to work properly. v dd monitoring requires 10.6s (typ) per measurement. temperature measurement the MAX1253/max1254 perform temperature measure- ment by measuring the voltage across a diode-con- nected transistor at two different current levels. the following equation illustrates the algorithm used for temperature calculations: where: v high = sensor-diode voltage with high current flowing (i high ) v low = sensor-diode voltage with low current flowing (i low ) q = charge of electron = 1.602 ? 10 -19 coulombs k = boltzman constant = 1.38 ? 10 -23 j/k n = ideality factor (slightly greater than 1) temperature v v x high low = ? ? ? ? ? ? () - q k nxln i i high low v x current data register content x v dd ref = ? ? ? ? ? ? 2 4096 (__ _ ) c3 c2 c1 c0 a2 a1 a0 sclk din dout c3 c2 c1 c0 a2 a1 a0 a3 a3 cs t pu+conv figure 9. manual conversion timing without reading data
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor 24 ______________________________________________________________________________________ the temperature measurement process is fully auto- mated in the MAX1253/max1254. all steps are sequenced and executed by the MAX1253/max1254 each time an input channel (or an input channel pair) configured for temperature measurement is scanned. the resulting 12-bit, two s complement number repre- sents the sensor temperature in degrees celsius, with 1 lsb = +0.125 c. the MAX1253/max1254 support both single-ended and differential temperature measurements. applications information setting up the MAX1253/max1254 subsystem the MAX1253/max1254 are autonomous subsystems, requiring only initialization to scan, convert, and monitor the voltage signals or the temperature sensors con- nected to their input channels. for simple applications, using any number of the input channels and any combination of voltage/temperature and unipolar/differential, with no interrupt generation required, use the following intitialization procedure: issue a write global configuration registers com- mand. this is a single, 5-byte write operation that con- figures the input channels, enables the channels to be used, sets the sample wait time between scans, con- figures the interrupt output int, selects the reference mode, and starts the automatic scan mode. see the write global configuration registers command sec- tion, table 2, and tables 5 10. immediately after the global configuration register is loaded, the MAX1253/max1254 begin to update the current data registers. acquire conversion data from the MAX1253/max1254 by issuing a command to read a specific channel with the read current data register for selected channel command. read all current data registers at once with the read current data registers for all channels command. for more complex applications, the monitoring and interrupt generation features of the MAX1253/max1254 require a second step of initialization. each enabled channel to be monitored requires configuration using a write configuration register for selected channel com- mand. each command is a 5-byte write that sets the upper and lower fault thresholds, the number of faults for an alarm before an interrupt is generated, and an aver- age algorithm parameter if the application requires input signal filtering. applications can read the current data registers and respond to interrupts signaled by the int output (see the servicing interrupts at int section). all the MAX1253/max1254 registers can be verified by reading back written data, including the configuration registers. this feature is useful for development and testing (see table 2). power-up/reset defaults summary setup register power-up/reset defaults at initial power-up or after a reset command, the setup register resets to 00 hex. consequently, the MAX1253/max1254 are configured as follows: sample wait time is 0s. int output is open drain and outputs an active-low signal to signify an alarm. manual conversion mode. external reference for voltage measurements. table 15. power-up/reset defaults summary register bit range power-up/reset state comments setup b0 to b7 all 0s see setup register power-up/reset defaults channel enable b0 to b11 all 1s all channels (int/ext) enabled input configuration b0 to b11 all 0s all single-ended voltage inputs alarm register b0 to b23 all 0s no alarms set channel configuration b0 to b7 all 0s faults = 0, no averaging upper threshold b0 to b9 all 1s all upper thresholds max range lower threshold b0 to b9 all 0s all lower thresholds min range current data registers b0 to b9 200hex set at midrange
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor ______________________________________________________________________________________ 25 channel-enable register power-up/reset defaults at power-on or after a reset command, the channel- enable register resets to ff hex, enabling all channels: the internal temperature sensor, the v dd monitor, and ain0 ain7. input configuration register power-up/reset defaults at power-on or after a reset command, the input con- figuration register resets to 00 hex, configuring ain0 ain7 for single-ended voltage measurement. alarm register power-up/reset defaults at power-on or after a reset command, the alarm reg- ister is reset to 000000 hex, indicating that no alarm condition exists. current data register power-up/reset defaults at power-on or after a reset command, each chan- nel s current data register is reset to 800 hex. upper threshold register power-up/reset defaults at power-on or after a reset command, each chan- nel's upper threshold register is reset to fff hex. this state effectively disables the upper threshold. lower threshold register power-up/reset defaults at power-on or after a reset command, each chan- nel's lower threshold register is reset to 000 hex. this state effectively disables the lower threshold. channel configuration register power-up/reset defaults at power-on or after a reset command, each chan- nel's configuration register is reset to 000 hex, which configures the fault bits to cause an alarm to occur on the first overrange or underrange condition and dis- ables averaging. computing data throughput the MAX1253/max1254 throughput rate depends on the number of enabled channels, their configuration (temperature or voltage), and the reference mode. voltage measurements require 10.6s (typ) to com- plete, and temperature measurements require 46s. channel pairs configured for differential measurements count as only one for throughput computation. the reference system takes 20s to power up in refer- ence mode 00 prior to each temperature measurement, 40s to power up in reference mode 01 after each sam- ple wait period (if sample wait time > 80s), and no power-up time in reference mode 10. the sampling period is calculated as follows: t sw =(t pu )+(n v )t conv[volt] +(n t )t conv[temp] +t wait where: t sw = all channels scan sampling period t pu = reference power-up time t conv[volt] = voltage-configured channel conversion time n v = number of voltage-configured channels t conv[temp] = temperature-configured channel conver- sion time n t = number of temperature-configured channels t wait = sample wait time the terms in the above equation are determined as shown above by the number of enabled channels, the input channel configuration (voltage vs. temperature), the sample wait time, and the reference mode. the fol- lowing calculation shows a numeric example: t sw = 40s + 8 x 10.6s + 2 x 46s + 395s = 611.8s 40s is the time required for the reference to power- up (reference mode = 00) every time the MAX1253/max1254 come out of automatic shut- down mode after a sample wait period. 8 x 10.6s is the time required for seven channels configured for voltage measurement and the v dd monitor. 2 x 46s is the time required for temperature mea- surement (46s for each temperature measurement (internal or external)). 395s is the sample wait time, set by bits b5, b6, b7 of the setup register (see tables 7 and 8). the MAX1253/max1254 use an internal clock for all conversions. the serial interface clock does not affect conversion time. performing eight single-ended remote channels tem- perature measurements, an internal temperature mea- surement, and an internal v dd measurement with a sample wait time of zero results in an average conver- sion rate of 24ksps or 2.4ksps per channel. performing eight single-ended voltage measurements, an internal temperature measurement, and an internal v dd measurement with sample wait time of zero results in an average conversion rate of 70ksps or 7ksps per channel.
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor 26 ______________________________________________________________________________________ automatic reference shutdown the MAX1253/max1254 enter an automatic shutdown mode when in reference mode 00 or when the sample wait is greater than 80s in reference mode 01. using either of these reference modes and a sample wait period as long as the application allows results in the lowest power consumption. temperature measurement the MAX1253/max1254 support both single-ended and differential temperature measurements. the design decision between the two types of measurements depends on the desired level of accuracy and on type and/or number of temperature sensors. the superior common-mode rejection and lower noise of the differ- ential mode reduces measurement errors and provides higher accuracy, while single-ended measurements require a lower number of connections, resulting in a simpler implementation and a higher number of moni- tored points for each MAX1253/max1254. differential temperature measurement connect the anode of a diode-connected transistor to the even input channel and the cathode to the odd input channel of an input pair configured for differential temperature measurement (ain0/ain1, ain2/ain3, ain4/ain5, or ain6/ain7). run the two sensor connec- tion lines parallel to each other with minimum spacing. this improves temperature measurement accuracy by minimizing the differential noise between the two lines, since they have equal exposure to most sources of noise. for further improved noise rejection, shield the two sensor connections by running them between ground planes, when available. configure the MAX1253/max1254 inputs for differential temperature measurement in the input configuration register (see tables 9 and 10) and enable the even channel number in the channel enable register (see table 4). single-ended temperature measurement connect the anode of a diode-connected transistor to the input channel and the cathode to ground. choose ground connections for sensors away from high-current return paths to avoid the introduction of errors caused by voltage drops in the board/system ground, which is the main drawback for single-ended measurements. practical options for better accuracy are the use of a star-configured subsystem ground or a signal ground plane; to isolate the anode sensor connection trace away from board and system noise sources; or to shield it with ground lines and ground planes (when available) to pre- vent accuracy degradation in the temperature measure- ments caused by magnetic/electric noise induction. configure the MAX1253/max1254 input used for single- ended temperature measurement in the input configura- tion register (see tables 9 and 10) and enable the analog input in the channel-enable register (see table 4). remote temperature sensor selection temperature-sensing accuracy depends on having a good-quality, diode-connected, small-signal transistor as a sensor. accuracy has been experimentally verified for 2n3904-type devices. the transistor must be a small-signal type with low base resistance. tight speci- fications for forward current gain (+50 to +150, for example) indicate that the manufacturer has good process controls and that the devices have consistent v be characteristics. cpu on-board sensors and other ics on-board temperature-sensing devices can also be used (see table 16 for recommended devices). table 16. remote sensor transistor manufacturers manufacturer model number central semiconductor (usa) cmpt3904 fairchild semiconductors (usa) mmbt3904 motorola (usa) mmbt3904 rohm semiconductor (japan) sst3904 siemens (germany) smb3904 zetex (england) fmmt3904ct-nd diodes inc. mmbt3904 output code full-scale transition 11....111 0 0 input voltage (lsb) zs = 0 fs = v ref 11....110 11....101 00....011 00....010 00....001 00....000 2 13 fs 1 lsb = v ref 4096 fs = 3/2 lsb figure 10. unipolar transfer function, full scale (fs) = v ref
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor ______________________________________________________________________________________ 27 transfer function figure 10 shows the nominal transfer function for single- ended or differential unipolar configured inputs, figure 11 illustrates the transfer function for differential bipolar conversions, and figure 12 shows temperature conver- sions. code transitions occur halfway between succes- sive-integer lsb values. output coding is binary, with 1 lsb = 610v (MAX1253) or 1mv (max1254) for unipo- lar and bipolar operation, and 1 lsb = +0.125 c (MAX1253/max1254) for temperature measurements. for unipolar operation, the 0 code level transition is at [1/2(v ref / 4096)]. the fff hex level transition is at [4094.5 (v ref / 4096)]. 1 lsb = v ref / 4096. layout, grounding, and bypassing for best performance, use pc boards. do not use wire- wrap boards. board layout should ensure that digital and analog signal lines are separated from each other. do not run analog and digital (especially clock) signals parallel to one another or run digital lines underneath the MAX1253/max1254 package. high-frequency noise in the v dd power supply can affect the MAX1253/max1254 performance. bypass the v dd sup- ply with a 0.1f capacitor from v dd to gnd, close to the v dd pin. minimize capacitor lead lengths for best supply-noise rejection. if the power supply is very noisy, connect a 10 ? resistor in series with the supply to improve power-supply filtering. definitions integral nonlinearity integral nonlinearity is the deviation of the values on the actual transfer function from a straight line. this straight line can be either a best-straight-line fit or a line drawn between the end points of the transfer function, once off- set and gain errors have been corrected. the static lineari- ty parameters for the MAX1253/max1254 are measured using the end-point-fit method. inl is specified as the maximum deviation in lsbs. differential nonlinearity (dnl) differential nonlinearity is the difference between an actual step width and the ideal value of 1 lsb. a dnl error specification of less than 1 lsb guarantees no missing codes and a monotonic transfer function. offset error the offset error is the difference between the ideal and the actual analog input value at the first transition of the adc, usually from digital code 0 to code 1 for straight binary output. for the MAX1253/max1254, the transi- tion between code 0 and code 1 should occur at an input voltage of 1/2 lsb, or 305v for the MAX1253 and 500v for the max1254. output code 011....111 temperature c 011....110 000....001 111....101 100....001 100....000 111....111 111....110 000....000 0 000....010 -256 c +255.875 c figure 12. temperature transfer function output code 011....111 input voltage (lsb) 011....110 000....001 111....101 100....001 100....000 111....111 111....110 000....000 0 000....010 -fs +fs - 1 lsb fs = zs = 0 v ref 2 -fs = -v ref 2 1 lsb = v ref 4096 figure 11. bipolar transfer function, full scale (fs) = v ref /2
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor 28 ______________________________________________________________________________________ gain error the gain error is the difference between the ideal and actual value of the analog input difference between the first and last transitions of the adc output. the first transition is from digital code 0 to code 1, and the last from code (2 n-2 ) to code (2 n-1 ), where n = number of adc bits for straight binary output code. for the MAX1253/max1254, the ideal difference in the input voltage between code transitions 0 to 1 and code tran- sitions 4094 to 4095 is 4094 x lsb. for the MAX1253, this is 2.5v - 2 x lsb = 2.498780v, and for the max1254, this is 4.096v - 2 x lsb = 4.094v. gain error is a dc specification, usually normalized to the fs ideal analog value and given in percent of fsr or ppm. signal-to-noise ratio for a waveform perfectly reconstructed from digital samples, signal-to-noise ratio (snr) is the ratio of the full-scale analog input (rms value) to the rms quantiza- tion error (residual error). the ideal theoretical minimum analog-to-digital noise is caused by quantization error only, results directly from the adc s resolution (n bits), and can be calculated with the following equation: snr = (6.02 x n + 1.76)db signal-to-noise plus distortion signal-to-noise plus distortion (sinad) is the ratio of the fundamental input frequency s rms amplitude to the rms equivalent of all other adc output signals: sinad (db) = 20 x log (signal rms / noise rms ) there are other noise sources besides quantization noise, including thermal noise, reference noise, clock jitter, etc. therefore, sinad is calculated by taking the ratio of the full-scale signal to the rms noise, which includes all spectral components minus the fundamen- tal and the first five harmonics. total harmonic distortion (thd) total harmonic distortion (thd) is the ratio of the rms sum of the first five harmonics of the input signal to the fundamental itself. this is expressed as: where v 1 is the fundamental rms value, and v 2 through v 5 are the rms values of the 2nd- through 5th- order harmonics, respectively. power-supply rejection power-supply rejection is the ratio between the change in the adc full-scale output to the change in power- supply voltage when the power-supply voltage is varied from its nominal value. it is specified in v/v or v/v. thd x vvvv v log = +++ () ? ? ? ? 20 2 2 3 2 4 2 5 2 1
MAX1253/max1254 stand-alone, 10-channel, 12-bit system monitors with internal temperature sensor and v dd monitor maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ____________________ 29 ? 2003 maxim integrated products printed usa is a registered trademark of maxim integrated products. reference temp sensor mux digital block channel registers global registers spi interface c v ref int spi i/f gnd v dd +v 48v ain0 ain1 ain2 ain3 ain4 ain5 ain6 ain7 remote temp adc power supply -5v +5v +3v MAX1253 max1254 typical operating circuit chip information transistor count: 89,473 process: 0.6m bicmos

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