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? 2002 microchip technology inc. ds21461b-page 1 tc7136/tc7136a features ? fast over range recovery, ensured first reading accuracy low temperature drift internal reference - tc7136: 70ppm/c (typ.) - tc7136a: 35ppm/c (typ.) zero reading with zero input low noise: 15 v p-p high resolution: 0.05% low input leakage current: 1pa (typ.)/10pa (max.) precision null detectors with true polarity at zero high-impedance differential input convenient 9v battery operation with low power dissipation: 500 w (typ.)/900 w(max.) applications thermometry bridge readouts: strain gauges, load cells, null detectors digital meters: voltage/current/ohms/power, ph digital scales, process monitors portable instrumentation device selection table general description the tc7136 and tc7136a are low power, 3-1/2 digit with liquid crystal display (lcd) drivers and analog-to- digital converters. these devices incorporate an "inte- grator output zero" phase, which enables over range recovery. the performance of existing tc7126, tc7126a and icl7126 based systems may be upgraded with minor changes to external, passive components. the tc7136a has an improved internal zener refer- ence voltage circuit which maintains the analog com- mon temperature drift to 35ppm/c (typical) and 75ppm/c (maximum). this represents an improve- ment of two to four times over similar 3-1/2 digit con- verters. the costly, space consuming external reference source may be removed. the tc7136 and tc7136a limit linearity error to less than 1 count on 200mv or 2v full scale ranges. the roll- over error (the difference in readings for equal magni- tude, but opposite polarity input signals) is below 1 count. high-impedance differential inputs offer 1pa leakage currents and a 10 12 ? input impedance. the differential reference input allows ratiometric measure- ments for ohms or bridge transducer measurements. the 15 v p-p noise performance ensures a "rock solid" reading. the auto-zero cycle enables a zero display readout for a 0v input. part number package temperature range tc7136 cpi 40-pin pdip 0 cto+70 c tc7136 ckw 44-pin pqfp 0 cto+70 c tc7136 clw 44-pin plcc 0 cto+70 c tc7136a cpi 40-pin pdip 0 cto+70 c tc7136a ckw 44-pin pqfp 0 cto+70 c tc7136a clw 44-pin plcc 0 cto+70 c low power 3-1/2 digit analog-to-digital converter
tc7136/tc7136a ds21461b-page 2 ? 2002 microchip technology inc. package type tc7136cpl tc7136acpl 1 2 3 4 osc1 5 6 7 8 9 10 11 12 test v ref + analog common c az v+ d 2 normal pin configuration 13 14 15 16 17 18 19 20 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 c 2 b 2 a 2 f 2 e 2 d 3 b 3 f 3 e 3 ab 4 10's 100's 1000's 100's osc2 osc3 v ref - c ref + c ref - v in + v in - v buff v int v- g 2 c 3 a 3 g 3 bp (backplane) pol (minus sign) tc7136rcpl tc7136arcpl 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 100's 1000's 100's reverse pin configuration 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 d 1 c 1 b 1 a 1 f 1 g 1 e 1 1's v+ d 2 c 2 b 2 a 2 f 2 e 2 d 3 b 3 f 3 e 3 ab 4 pol (minus sign) d 1 c 1 b 1 a 1 f 1 g 1 e 1 1's 10's osc1 test v ref + analog common c az osc2 osc3 v ref - c ref + c ref - v in + v in - v buff v int v- g 2 c 3 a 3 g 3 bp (backplane) nc = no internal connection 27 28 29 30 31 32 33 7 4 3 2 1 nc tc7136ckw tc7136ackw 12 13 14 15 17 18 g 2 44 43 42 41 39 38 40 ref hi analog common 16 37 az 36 buff 35 int 34 v- 19 20 21 22 d 3 26 8 25 9 24 10 23 11 in hi 5 6 c 3 osc3 test nc nc v+ d 2 c 2 b 2 a 2 f 2 e 2 nc osc2 osc1 ref lo c ref + c ref - in lo a 3 g 3 bp pol ab 4 e 3 f 3 b 3 33 34 35 36 37 38 39 13 10 9 8 7 analog common ref lo 18 19 20 21 23 24 ab 4 pol nc bp in hi nc in lo b 2 6543 144 2 a 1 osc1 22 43 osc2 42 osc3 41 test 40 ref hi 25 26 27 28 f 3 e 3 g 3 a 3 c 3 g 2 32 14 az 31 15 buff 30 16 int e 2 29 17 d 3 nc 11 12 nc c 2 d 2 f 2 a 2 b 3 tc7136clw tc7136aclw 44-pin plcc 40-pin pdip 44-pin pqfp 40-pin pdip v- b 1 c 1 d 1 v+ f 1 g 1 e 1 d 1 c 1 b 1 a 1 f 1 g 1 e 1 c ref + c ref -
? 2002 microchip technology inc. ds21461b-page 3 tc7136/tc7136a typical application v ref + tc7136 tc7136a 33 34 240k ? 10k ? 31 29 39 38 40 v ref - 0.47 f 0.1 f v- osc1 osc3 osc2 to analog common (pin 32) 1 conversion/sec c osc 560k ? 180k ? 0.15 f 0.01 f analog input + ? c ref - c ref + v in + v in - analog common v int v buff c az 20 21 1 segment drive 9-19 22-25 pol bp v+ minus sign backplane 28 50pf lcd 1m ? 27 30 32 35 36 9v + r osc 26
tc7136/tc7136a ds21461b-page 4 ? 2002 microchip technology inc. functional block diagram tc7136/a thousands hundreds tens units 4 39 osc2 v+ tes t 1 to switch clock 7-segment decode 40 38 osc3 osc1 control logic 26 500 ? data latch c ref - r int v c az v int 28 29 27 33 36 34 10 a 31 zi & az int az & de () 32 int 26 integrator to digital section de (+) de ( ? ) de (+) de ( ? ) analog common c ref + v in + v in - v buff c int v ref +v ref - zi & az c ref + 35 + ? lcd segment drivers 200 bp f osc v- v th = 1v v- + ? internal digital ground low tempco v ref comparator ? az zi v+ ? 2.8v 1 r osc c osc 7-segment decode 7-segment decode 21 typical segment input internal digital ground segment output v+ 0.5ma 2ma 6.2v lcd + ? 37
? 2002 microchip technology inc. ds21461b-page 5 tc7136/tc7136a 1.0 electrical characteristics absolute maximum ratings* supply voltage (v+ to v-)....................................... 15v analog input voltage (either input) (note 1) ... v+ to v- reference input voltage (either input)............ v+ to v- clock input .................................................test to v+ package power dissipation (t a 70c) (note 2) : plastic dip ................................................... 1.23w plastic quad flat package .......................... 1.00w plcc ........................................................... 1.23w operating temperature range: c devices.......................................... 0c to +70c i devices ........................................ -25c to +85c storage temperature range .............. -65c to +150c *stresses above those listed under "absolute maximum ratings" may cause permanent damage to the device. these are stress ratings only and functional operation of the device at these or any other conditions above those indicated in the operation sections of the specifications is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. tc7136 and tc7136a electrical specifications electrical characteristics: v s =9v,f clk =16khz,andt a = +25c, unless otherwise noted. symbol parameter min typ max unit test conditions input zero input reading -000.0 000.0 +000.0 digital reading v in = 0v, full scale = 200mv zero reading drift ? 0.2 1 v/c v in =0v,0c t a +70c ratiometric reading 999 999/1000 1000 digital reading v in =v ref ,v ref = 100mv nl non-linearity error ? 1 0.2 count full scale = 20mv or 2v max. deviation from best straight line e r rollover error -1 -1 0.2 1 count v in -=v in + 200mv e n noise ? 15 ? v p-p v in = 0v, full scale = 200mv i l input leakage current ? 1 10 pa v in =0v cmrr common mode rejection ratio ? 50 ? v/v v cm =1v,v in =0v,fullscale=200mv tc sf scale factor temperature coefficient ?1 5ppm/cv in =199mv,0c t a +70c ext. ref. temp. coeff. = 0ppm/c note 1: input voltages may exceed supply voltages when input current is limited to 100 a. 2: dissipation rating assumes device is mounted with all leads soldered to pc board. 3: refer to "differential input" discussion. 4: backplane drive is in phase with segment drive for "off" segment and 180 out-of-phase for "on" segment. frequency is 20 times conversion rate. average dc component is less than 50mv. 5: see "typical application". 6: a 48khz oscillator increases current by 20 a (typical). common current not included.
tc7136/tc7136a ds21461b-page 6 ? 2002 microchip technology inc. analog common v ctc analog common temperature coefficient 250k ? between common and v+ tc7136a ? 35 75 ppm/c 0c t a +70c tc7136 ? 70 150 ppm/c "c" commercial temp. range devices tc7136a ? 35 100 ppm/c -25c t a +85c tc7136 ? 70 150 ppm/c "i" industrial temp. range devices v c analog common voltage 2.7 3.05 3.35 v 250k ? between common and v+ lcd drive v sd lcd segment drive voltage 4 5 6 v p-p v+ to v- = 9v v bd lcd backplane drive voltage 4 5 6 v p-p v+ to v- = 9v power supply i s power supply current ? 70 100 av in =0v,v+tov-=9v (note 6) tc7136 and tc7136a electrical specifications (continued) electrical characteristics: v s =9v,f clk =16khz,andt a = +25c, unless otherwise noted. symbol parameter min typ max unit test conditions note 1: input voltages may exceed supply voltages when input current is limited to 100 a. 2: dissipation rating assumes device is mounted with all leads soldered to pc board. 3: refer to "differential input" discussion. 4: backplane drive is in phase with segment drive for "off" segment and 180 out-of-phase for "on" segment. frequency is 20 times conversion rate. average dc component is less than 50mv. 5: see "typical application". 6: a 48khz oscillator increases current by 20 a (typical). common current not included.
? 2002 microchip technology inc. ds21461b-page 7 tc7136/tc7136a 2.0 pin descriptions thedescriptionsofthepinsarelistedintable2-1. table 2-1: pin description pin number (40-pin pdip) normal (reverse) symbol description 1 (40) v+ positive supply voltage. 2(39)d 1 activates the d section of the units display. 3(38)c 1 activates the c section of the units display. 4(37)b 1 activates the b section of the units display. 5(36)a 1 activates the a section of the units display. 6(35)f 1 activates the f section of the units display. 7(34)g 1 activates the g section of the units display. 8(33)e 1 activates the e section of the units display. 9(32)d 2 activates the d section of the tens display. 10 (31) c 2 activates the c section of the tens display. 11 (30) b 2 activates the b section of the tens display. 12 (29) a 2 activates the a section of the tens display. 13 (28) f 2 activates the f section of the tens display. 14 (27) e 2 activates the e section of the tens display. 15 (26) d 3 activates the d section of the hundreds display. 16 (25) b 3 activates the b section of the hundreds display. 17 (24) f 3 activates the f section of the hundreds display. 18 (23) e 3 activates the e section of the hundreds display. 19 (22) ab 4 activates both halves of the 1 in the thousands display. 20 (21) pol activates the negative polarity display. 21 (20) bp backplane drive output. 22 (19) g 3 activates the g section of the hundreds display. 23 (18) a 3 activates the a section of the hundreds display. 24 (17) c 3 activates the c section of the hundreds display. 25 (16) g 2 activates the g section of the tens display. 26 (15) v- negative power supply voltage. 27 (14) v int the integrating capacitor should be selected to give the maximum voltage swing that ensures component tolerance buildup will not allow the integrator output to sat- urate. when analog common is used as a reference and the conversion rate is 3 readings per second, a 0.047 f capacitor may be used. the capacitor must have a low dielectric constant to prevent rollover errors. see section 6.3, integrating capacitor for additional details. 28 (13) v buff integration resistor connection. use a 180k ? for a 20mv full scale range and a 1.8m ? for 2v full scale range. 29 (12) c az the size of the auto-zero capacitor influences the system noise. use a 0.47 f capacitor for a 200mv full scale and a 0.1 f capacitor for a 2v full scale. see section 6.1, auto-zero capacitor for more details. 30 (11) v in - the low input signal is connected to this pin. 31 (10) v in + the high input signal is connected to this pin. 32 (9) analog common this pin is primarily used to set the analog common mode voltage for battery operation, or in systems where the input signal is referenced to the power supply. see section 7.3, analog common for more details. it also acts as a reference voltage source. 33 (8) c ref -seepin34.
tc7136/tc7136a ds21461b-page 8 ? 2002 microchip technology inc. 34 (7) c ref +a0.1 f capacitor is used in most applications. if a large common mode voltage exists (for example, the v in - pin is not at analog common) and a 200mv scale is used, a 1 f capacitor is recommended, which will hold the rollover error to 0.5 count. 35 (6) v ref -seepin36. (5) v ref + the analog input required to generate a full scale output (1999 counts). place 100mv between pins 35 and 36 for 199.9mv full scale. place 1v between pins 35 and 36 for 2v full scale. see section 6.6, reference voltage. 36 (4) test lamp test. when pulled high (to v+), all segments will be turned on and the display should read -1888 . it may also be used as a negative supply for externally generated decimal points. see section 7.4, test for additional information. 37 (3) osc3 see pin 40. 38 (2) osc2 see pin 40. 39 (1) osc1 pins 40, 39 and 38 make up the oscillator section. for a 48khz clock (3 readings per second), connect pin 40 to the junction of a 180k ? resistor and a 50pf capacitor. the 180k ? resistor is tied to pin 39 and the 50pf capacitor is tied to pin 38. table 2-1: pin description (continued) pin number (40-pin pdip) normal (reverse) symbol description
? 2002 microchip technology inc. ds21461b-page 9 tc7136/tc7136a 3.0 detailed description (all pin designations refer to 40-pin pdip.) 3.1 dual slope conversion principles the tc7136/a is a dual slope, integrating analog-to- digital converter. an understanding of the dual slope conversion technique will aid in following detailed tc7136/a operational theory. the conventional dual slope converter measurement cycle has two distinct phases (see figure 3-1). 1. input signal integration 2. reference voltage integration (de-integration) the input signal being converted is integrated for a fixed time period (t si ), measured by counting clock pulses. an opposite polarity constant reference voltage is then integrated until the integrator output voltage returns to zero. the reference integration time is directly proportional to the input signal (t ri ). in a simple dual slope converter, a complete conver- sion requires the integrator output to "ramp up" and "ramp down." a simple mathematical equation relates the input signal, reference voltage, and integration time: equation 3-1: for a constant v in : equation 3-2: figure 3-1: basic dual slope converter figure 3-2: normal mode rejection of dual slope converter the dual slope converter accuracy is unrelated to the integrating resistor and capacitor values, as long as they are stable during a measurement cycle. noise immunity is an inherent benefit. noise spikes are inte- grated or averaged to zero during integration periods. integrating adcs are immune to the large conversion errors that plague successive approximation convert- ers in high noise environments. interfering signals with frequency components at multiples of the averaging period will be attenuated. integrating adcs commonly operate with the signal integration period set to a multiple of the 50hz/60hz power line period. 1 rc -------- - v in t () t d 0 t si v r t ri rc ------------ = where: v r = reference voltage t si = signal integration time (fixed) t ri = reference voltage integration time (variable) v in v r t ri t si ------- - = + ? ref voltage analog input signal + ? display switch driver control logic integrator output clock counter polarity control phase control v in v ref v in 1/2 v ref variable reference integrate time fixed signal integrate time integrator comparator c int 30 20 10 0 normal mode rejection (db) 0.1/t 1/t 10/t in p ut fre q uenc y t = measured period
tc7136/tc7136a ds21461b-page 10 ? 2002 microchip technology inc. 4.0 analog section in addition to the basic integrate and de-integrate dual slope cycles discussed above, the tc7136 and tc7136a designs incorporate an "integrator output zero cycle" and an "auto-zero cycle." these additional cycles ensure the integrator starts at 0v (even after a severe over range conversion) and that all offset volt- age errors (buffer amplifier, integrator and comparator) are removed from the conversion. a true digital zero reading is assured without any external adjustments. a complete conversion consists of four distinct phases: 1. integrator output zero phase 2. auto-zero phase 3. signal integrate phase 4. reference de-integrate phase 4.1 integrator output zero phase this phase ensures the integrator output is at 0v before the system zero phase is entered. this ensures that true system offset voltages will be compensated for, even after an over range conversion. the count for this phase is a function of the number of counts required by the de-integrate phase. the count lasts from 11 to 140 counts for non over range conversions and from 31 to 640 counts for over range conversions. 4.2 auto-zero phase during the auto-zero phase, the differential input signal is disconnected from the circuit by opening internal analog gates. the internal nodes are shorted to analog common (ground) to establish a zero input condition. additional analog gates close a feedback loop around the integrator and comparator. this loop permits com- parator offset voltage error compensation. the voltage level established on c az compensates for device offset voltages. the auto-zero phase residual is typically 10 vto15 v. the auto-zero duration is from 910 to 2900 counts for non over range conversions and from 300 to 910 counts for over range conversions. 4.3 signal integration phase the auto-zero loop is entered and the internal differen- tial inputs connect to v in + and v in -. the differential input signal is integrated for a fixed time period. the tc7136/a signal integration period is 1000 clock peri- ods or counts. the externally set clock frequency is divided by four before clocking the internal counters. the integration time period is: equation 4-1: the differential input voltage must be within the device common mode range when the converter and mea- sured system share the same power supply common (ground). if the converter and measured system do not share the same power supply common, v in - should be tied to analog common. polarity is determined at the end of signal integrate phase. the sign bit is a true polarity indication, in that signals less than 1lsb are correctly determined. this allows precision null detection, limited only by device noise and auto-zero residual offsets. 4.4 reference integrate phase the third phase is reference integrate or de-integrate. v in - is internally connected to analog common and v in + is connected across the previously charged refer- ence capacitor. circuitry within the chip ensures that the capacitor will be connected with the correct polarity to cause the integrator output to return to zero. the time required for the output to return to zero is propor- tional to the input signal and is between 0 and 2000 internal clock periods. the digital reading displayed is: equation 4-2: figure 4-1: conversion timing during normal operation figure 4-2: conversion timing during over range operation t si = x 1000 4 f osc where f osc = external clock frequency. 1000 v in v ref ---------------- = int dent zi az 4000 910-2900 1-2000 1000 11-140 az 4000 zi deint int 1000 2001-2090 31-640 300-910
? 2002 microchip technology inc. ds21461b-page 11 tc7136/tc7136a 5.0 digital section the tc7136/a contains all the segment drivers neces- sary to directly drive a 3-1/2 digit lcd. an lcd back- plane driver is included. the backplane frequency is the external clock frequency divided by 800. for three conversions per second, the backplane frequency is 60hz with a 5v nominal amplitude. when a segment driver is in phase with the backplane signal, the seg- ment is off. an out-of-phase segment drive signal causes the segment to be on, or visible. this ac drive configuration results in negligible dc voltage across each lcd segment, ensuring long lcd life. the polar- ity segment driver is on for negative analog inputs. if v in +andv in - are reversed, this indicator would reverse. on the tc7136/a, when the test pin is pulled to v+, all segments are turned on. the display reads -1888 . during this mode, the lcd segments have a constant dc voltage impressed. the display font and segment drive assignment are shown in figure 5-1. figure 5-1: display font and segment assignment 5.1 system timing the oscillator frequency is divided by 4 prior to clocking the internal decade counters. the four-phase mea- surement cycle takes a total of 4000 counts, or 16,000 clock pulses. the 4000 count cycle is independent of input signal magnitude. each phase of the measurement cycle has the following length: 1. auto-zero phase: 3000 to 2900 counts (1200 to 11,600 clock pulses) 2. signal integrate: 1000 counts (4000 clock pulses) this time period is fixed. the integration period is: equation 5-1: 3. reference integrate: 0 to 2000 counts 4. zero integrator: 11 to 640 counts the tc7136 is a drop-in replacement for the tc7126 and icl7126. the tc7136a offers a greatly improved internal reference temperature coefficient. minor com- ponent value changes are required to upgrade existing designs and improve the noise performance. 6.0 component value selection 6.1 auto-zero capacitor (c az ) the c az capacitor size has some influence on system noise. a 0.47 f capacitor is recommended for 200mv full scale applications, where 1lsb is 100 v. a 0.1 f capacitor is adequate for 2v full scale applications. a mylar type dielectric capacitor is adequate. 6.2 reference voltage capacitor (c ref ) the reference voltage, used to ramp the integrator out- put voltage back to zero during the reference integrate phase, is stored on c ref .a0.1 f capacitor is accept- able when v ref - is tied to analog common. if a large common mode voltage exists (v ref - analog com- mon) and the application requires a 200mv full scale, increase c ref to 1 f.rollovererrorwillbeheldtoless than 0.5 count. a mylar type dielectric capacitor is adequate. 6.3 integrating capacitor (c int ) c int should be selected to maximize integrator output voltage swing without causing output saturation. ana- log common will normally supply the differential voltage reference in this case, a 2v full scale integrator output swing is satisfactory. for 3 readings per second (f osc = 48khz), a 0.047 f value is suggested. for one reading per second, 0.15 f is recommended. if a different oscillator frequency is used, c int must be changed in inverse proportion to maintain the nominal 2v integrator swing. note: do not leave the display in this mode for more than several minutes. lcds may be destroyed if operated with dc levels for extended periods. display font 1000's 100's 10's 1's where: t si = 4000 1 f osc ? ? ? ? f osc is the externally set clock frequency.
tc7136/tc7136a ds21461b-page 12 ? 2002 microchip technology inc. an exact expression for c int is: equation 6-1: c int must have low dielectric absorption to minimize rollover error. a polypropylene capacitor is recommended. 6.4 integrating resistor (r int ) the input buffer amplifier and integrator are designed with class a output stages. the output stage idling cur- rent is 6 a. the integrator and buffer can supply 1 a drive currents with negligible linearity errors. r int is chosen to remain in the output stage linear drive region, but not so large that pc board leakage currents induce errors. for a 200mv full scale, r int is 180k ? .a 2v full scale requires 1.8m ? (see table 6-1). table 6-1: note: f osc = 48khz (3 reading per sec). r osc =180k ?, c osc =50pf. 6.5 oscillator components c osc should be 50pf. r osc is selected from the equation: equation 6-2: note that f osc is 4 to generate the tc7136a's inter- nal clock. the backplane drive signal is derived by dividing f osc by 800. to achieve maximum rejection of 60hz noise pickup, the signal integrate period should be a multiple of 60hz. oscillator frequencies of 240khz, 120khz, 80khz, 60khz, 40khz, etc. should be selected. for 50hz rejection, oscillator frequencies of 200khz, 100khz, 66-2/3khz, 50khz, 40khz, etc. would be suit- able. note that 40khz (2.5 readings per second) will reject both 50hz and 60hz. 6.6 reference voltage selection a full scale reading (2000 counts) requires the input signal be twice the reference voltage. note: *v ref =2v ref. in some applications, a scale factor other than unity may exist between a transducer output voltage and the required digital reading. assume, for example, a pres- sure transducer output for 2000 lb/in 2 is 400mv. rather than dividing the input voltage by two, the reference voltage should be set to 200mv. this permits the trans- ducer input to be used directly. the differential refer- ence can also be used when a digital zero reading is required, when v in is not equal to zero. this is common in temperature measuring instrumentation. a compen- sating offset voltage can be applied between analog common and v in -. the transducer output is connected between v in + and analog common. component value nominal full scale voltage 200mv 2v c az 0.47 f0.1 f r int 180k ? 1.8m ? c int 0.047 f 0.047 f (4000) 1 f osc ? ? ? ? c int = v fs r int ? ? ? ? v int where: f osc = clock frequency at pin 38 v fs = full scale input voltage r int = integrating resistor v int = desired full scale integrator output swing required full scale voltage* v ref 200mv 100mv 2v 1v f osc = 0.45 rc
? 2002 microchip technology inc. ds21461b-page 13 tc7136/tc7136a 7.0 device pin functional description 7.1 differential signal inputs v in +(pin31),v in -(pin30) the tc7136/a is designed with true differential inputs and accepts input signals within the input stage com- mon mode voltage range (v cm ). the typical range is v+ ? 1v to v- + 1v. common mode voltages are removed from the system when the tc7136a operates from a battery or floating power source (isolated from measured system), common mode voltage removed in battery operation with v in = analog common and v in - is connected to analog common (v com )(see figure 7-1). figure 7-1: common mode voltage removed in battery operation with v in = analog common in systems where common mode voltages exist, the 86db common mode rejection ratio minimizes error. common mode voltages do, however, affect the inte- grator output level. a worst case condition exists if a large positive v cm exists in conjunction with a full scale negative differential signal. the negative signal drives the integrator output positive along with v cm (see figure 7-2.) for such applications, the integrator out- put swing can be reduced below the recommended 2v full scale swing. the integrator output will swing within 0.3v of v+ or v- without increased linearity error. figure 7-2: common mode voltage reduces available integrator swing (v com v in ) 7.2 differential reference v ref +(pin36),v ref -(pin35) the reference voltage can be generated anywhere within the v+ to v- power supply range. to prevent rollover type errors being induced by large common mode voltages, c ref should be large com- pared to stray node capacitance. the tc7136/a offers a significantly improved analog common temperature coefficient. this potential provides a very stable volt- age, suitable for use as a voltage reference. the temperature coefficient of analog common is typically 35ppm/c. 7.3 analogcommon(pin32) the analog common pin is set at a voltage potential approximately 3v below v+. the potential is between 2.7v and 3.35v below v+. analog common is tied inter- nally to an n-channel fet, capable of sinking 100 a. this fet will hold the common line at 3v below v+ if an external load attempts to pull the common line toward v+. analog common source current is limited to 1 a. analog common is, therefore, easily pulled to a more negative voltage (i.e., below v+ ? 3v). v buf c az v int bp pol segment drive osc1 osc3 osc2 v- v+ v ref + v ref - analog common v- v+ v+ gnd gnd measured system power source 9v lcd tc7136 tc7136a + v- v+ v- r i + ? v in c i integrator v i = [ [ v cm = v in input buffer c i = integration capacitor r i = integration resistor 4000 f osc t i = integration time = where: v i ? + ? + t i c i v cm
tc7136/tc7136a ds21461b-page 14 ? 2002 microchip technology inc. the tc7136/a connects the internal v in + and v in - inputs to analog common during the auto-zero phase. during the reference integrate phase, v in - is connected to analog common. if v in - is not externally connected to analog common, a common mode voltage exists, but is rejected by the converter's 86db common mode rejection ratio. in battery operation, analog common and v in - are usually connected, removing common mode voltage concerns. in systems where v in - is con- nected to the power supply ground or to a given voltage, analog common should be connected to v in -. the analog common pin serves to set the analog sec- tion reference, or common point. the tc7136a is spe- cifically designed to operate from a battery, or in any measurement system where input signals are not refer- enced (float), with respect to the tc7136a power source. the analog common potential of v+ ? 3v gives a 7v end of battery life voltage. the common potential has a 0.001%/% voltage coefficient. with sufficiently high total supply voltage (v+ ? v- > 7v), analog common is a very stable poten- tial with excellent temperature stability (typically 35ppm/c for tc7136a. this potential can be used to generate the tc7136a's reference voltage. an external voltage reference will be unnecessary in most cases, because of the 35ppm/c temperature coefficient. see section 7.5, tc7136a internal voltage reference discussion. 7.4 test (pin 37) the test pin potential is 5v less than v + . test may be used as the negative power supply connection for external cmos logic. the test pin is tied to the inter- nally generated negative logic supply through a 500 ? resistor. the test pin load should not be more than 1ma. see section 8.0, typical applications for addi- tional information on using test as a negative digital logic supply. if test is pulled high (to v+), all segments plus the minus sign will be activated. do not operate in this mode for more than several minutes. with test = v+, the lcd segments are impressed with a dc voltage which will destroy the lcd. 7.5 tc7136a internal voltage reference the tc7136 analog common voltage temperature sta- bility has been significantly improved (figure 7-3). the "a" version of the industry standard tc7136 device allows users to upgrade old systems and design new systems without external voltage references. external r and c values do not need to be changed; however, noise performance will be improved by increasing c az (see section 6.1, auto-zero capacitor). figure 7-4 shows analog common supplying the necessary voltage reference for the tc7136/a. figure 7-3: analog common temperature coefficient figure 7-4: tc7136a internal voltage reference connection typical maximum maximum typical typical no maximum specified 200 180 160 140 120 100 80 60 40 20 0 analog common temperature coefficient (ppm/ c) tc7136 tc7136a icl7136 v- analog common tc7136 tc7136a v ref + 32 35 36 26 240k ? 10k ? v ref - v ref 1 + 9v set v ref = 1/2 v ref v+
? 2002 microchip technology inc. ds21461b-page 15 tc7136/tc7136a 8.0 typical applications 8.1 liquid crystal display sources several manufacturers supply standard lcds to inter- face with the tc7136a 3-1/2 digit analog-to-digital converter. note: contact lcd manufacturer for full product listing/ specifications. 8.2 decimal point and annunciator drive the test pin is connected to the internally generated digital logic supply ground through a 500 ? resistor. the test pin may be used as the negative supply for exter- nal cmos gate segment drivers. lcd annunciators for decimal points, low battery indication, or function indi- cation may be added without adding an additional sup- ply. no more than 1ma should be supplied by the test pin; its potential is approximately 5v below v+. 8.3 ratiometric resistance measurements the tc7136a's true differential input and differential reference make ratiometric readings possible. in ratio- metric operation, an unknown resistance is measured with respect to a known standard resistance. no accurately defined reference voltage is needed. the unknown resistance is put in series with a known standard and a current passed through the pair. the voltage developed across the unknown is applied to the input and the voltage across the known resistor applied to the reference input. if the unknown equals the stan- dard, the display will read 1000. the displayed reading can be determined from the following expression: equation 8-1: the display will over range for: r unknown 2xr standard figure 8-1: decimal point and annunciator drives manufac. address/phone representative part numbers* crystaloid electronics 5282 hudson dr. hudson, oh 44236 216-655-2429 c5335, h5535, t5135, sx440 and 720 palomar ave. sunnyvale, ca 94086 408-523-8200 fe 0201, 0501 fe 0203, 0701 fe 2201 vgi, inc. 1800 vernon st. ste.2, roseville, ca 95678 916-783-7878 i1048, i1126 hamlin, inc. 612 e. lake st. lake mills, wi 53551 414-648-2361 00 3902, 3933, 3903 displayed(reading) = r unknown r standard x 1000 v+ v+ tc7136 tc7136a v+ v+ tc7136 tc7136a 4049 4030 bp test bp test gnd gnd to lcd decimal point to lcd backplane to lcd decimal point decimal point select 21 37 multiple decimal point or annunciator driver simple inverter for fixed decimal point or display annunciator
tc7136/tc7136a ds21461b-page 16 ? 2002 microchip technology inc. figure 8-2: low parts count ratiometric resistance measurement figure 8-3: temperature sensor figure 8-4: positive temperature coefficient resistor temperature sensor v ref + v ref - v in + v in - analog common tc7136 tc7136a lcd r standard r unknown v+ tc7136 tc7136a v+ v- v in - v in + v ref + v ref - common 50k ? r 2 160k ? 300k ? 300k ? r 1 50k ? 1n4148 sensor 9v + tc7136 tc7136a v+ v- v in - v in + v ref + v ref - common 5.6k ? 160k ? r 2 20k ? 1n4148 9v r 1 20k ? + r 3 0.7%/ c ptc
? 2002 microchip technology inc. ds21461b-page 17 tc7136/tc7136a 9.0 packaging information 9.1 package marking information package marking data not available at this time. 9.2 taping form component taping orientation for 44-pin pqfp devices user direction of feed pin 1 standard reel component orientation for tr suffix device w p package carrier width (w) pitch (p) part per full reel reel size 44-pin pqfp 24 mm 16 mm 500 13 in carrier tape, number of components per reel and reel size note: drawing does not represent total number of pins. pin 1 component taping orientation for 44-pin plcc devices user direction of feed standard reel component orientation for tr suffix device note: drawing does not represent total number of pins. w p package carrier width (w) pitch (p) part per full reel reel size 44-pin plcc 32 mm 24 mm 500 13 in carrier tape, number of components per reel and reel size
tc7136/tc7136a ds21461b-page 18 ? 2002 microchip technology inc. 9.3 package dimensions dimensions: inches (mm) 2.065 (52.45) 2.027 (51.49) .200 (5.08) .140 (3.56) .150 (3.81) .115 (2.92) .070 (1.78) .045 (1.14) .022 (0.56) .015 (0.38) .110 (2.79) .090 (2.29) .555 (14.10) .530 (13.46) .610 (15.49) .590 (14.99) .015 (0.38) .008 (0.20) .700 (17.78) .610 (15.50) .040 (1.02) .020 (0.51) 40-pin pdip (wide) pin 1 3 min. dimensions: inches (mm) .695 (17.65) .685 (17.40) .656 (16.66) .650 (16.51) .656 (16.66) .650 (16.51) .021 (0.53) .013 (0.33) .032 (0.81) .026 (0.66) .630 (16.00) .591 (15.00) .120 (3.05) .090 (2.29) .180 (4.57) .165 (4.19) .695 (17.65) .685 (17.40) .050 (1.27) typ. .020 (0.51) min. pin 1 44-pin plcc
? 2002 microchip technology inc. ds21461b-page 19 tc7136/tc7136a 9.3 package dimensions (continued) dimensions: inches (mm) .557 (14.15) .537 (13.65) .398 (10.10) .390 (9.90) .031 (0.80) typ. .018 (0.45) .012 (0.30) .398 (10.10) .390 (9.90) .010 (0.25) typ. .096 ( 2.45 ) max. .557 (14.15) .537 (13.65) .083 (2.10) .075 (1.90) .041 (1.03) .026 (0.65) 7 max. .009 (0.23) .005 (0.13) 44-pin pqfp pin 1
tc7136/tc7136a ds21461b-page 20 ? 2002 microchip technology inc. sales and support data sheets products supported by a preliminary data sheet may have an errata sheet describing minor operational differences and recom- mended workarounds. to determine if an errata sheet exists for a particular device, please contact one of the following: 1. your local microchip sales office 2. the microchip corporate literature center u.s. fax: (480) 792-7277 3. the microchip worldwide site (www.microchip.com) please specify which device, revision of silicon and data sheet (include literature #) you are using. new customer notification system register on our web site (www.microchip.com/cn) to receive the most current information on our products.
? 2002 microchip technology inc. ds21461b-page 21 tc7136/tc7136a information contained in this publication regarding device applications and the like is intended through suggestion only and may be superseded by updates. it is your responsibility to ensure that your application meets with your specifications. no representation or warranty is given and no liability is assumed by microchip technology incorporated with respect to the accuracy or use of such information, or infringement of patents or other intellectual property rights arising from such use or otherwise. use of microchip?s products as critical com- ponents in life support systems is not authorized except with express written approval by microchip. no licenses are con- veyed, implicitly or otherwise, under any intellectual property rights. trademarks the microchip name and logo, the microchip logo, filterlab, k ee l oq ,microid, mplab,pic,picmicro,picmaster, picstart, pro mate, seeval and the embedded control solutions company are registered trademarks of microchip tech- nology incorporated in the u.s.a. and other countries. dspic, economonitor, fansense, flexrom, fuzzylab, in-circuit serial programming, icsp, icepic, microport, migratable memory, mpasm, mplib, mplink, mpsim, mxdev, picc, picdem, picdem.net, rfpic, select mode and total endurance are trademarks of microchip technology incorporated in the u.s.a. serialized quick turn programming (sqtp) is a service mark of microchip technology incorporated in the u.s.a. all other trademarks mentioned herein are property of their respective companies. ? 2002, microchip technology incorporated, printed in the u.s.a., all rights reserved. printed on recycled paper. microchip received qs-9000 quality system certification for its worldwide headquarters, design and wafer fabrication facilities in chandler and tempe, arizona in july 1999 and mountain view, california in march 2002. the company?s quality system processes and procedures are qs-9000 compliant for its picmicro ? 8-bit mcus, k ee l oq ? code hopping devices, serial eeproms, microperipherals, non-volatile memory and analog products. in addition, microchip?s quality system for the design and manufacture of development systems is iso 9001 certified.
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