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3-203 telcom semiconductor, inc. 7 6 5 4 3 1 2 8 3-1/2 digit analog-to-digital converters with hold v ref + tc7116/a 9v v ref 33 34 24 k w 1 k w 31 29 36 39 38 40 0.47 ? 0.1 ? v 1 osc 3 osc 2 osc to analog common (pin 32) 3 conversions/sec c osc 100 k w 47 k w 0.22 ? 0.01 ? analog input + c ref c ref + v in + v in analog common v int v buff c az 20 21 35 segment drive 2?9 22?5 pol bp/gnd v + minus sign backplane drive 28 r osc 100 pf lcd display (tc7116/7116a) or common anode led display (tc7117/7117a) 1 m w 27 30 32 hldr display hold 100 mv 1 26 tc7117/a + features n low temperature drift internal reference tc7116/tc7117 ............................. 80 ppm/ c typ tc7116a/tc7117a ........................ 20 ppm/ c typ n display hold function n directly drives lcd or led display n guaranteed zero reading with zero input n low noise for stable display ......... 2v or 200 mv full-scale range (fsr) n auto-zero cycle eliminates need for zero adjustment potentiometer n true polarity indication for precision null applications n convenient 9v battery operation (tc7116/tc7116a) n high impedance cmos differential inputs .... 10 12 w n low power operation .................................... 10 mw general description the tc7116a/tc7117a are 3-1/2 digit cmos analog- to-digital converters (adcs) containing all the active components necessary to construct a 0.05% resolution measurement system. seven-segment decoders, polarity and digit drivers, voltage reference, and clock circuit are integrated on-chip. the tc7116a drives liquid crystal displays (lcds) and includes a backplane driver. the tc7117a drives common anode light emitting diode (led) displays directly with an 8-ma drive current per segment. these devices incorporate a display hold (hldr) function. the displayed reading remains indefinitely, as long as hldr is held high. conversions continue, but output data display latches are not updated. the reference low input (v C ref ) is not available as it is with the tc7106/ 7107. v C ref is tied internally to analog common in the tc7116a/7117a devices. the tc7116a/7117a reduces linearity error to less than 1 count. roll-over error (the difference in readings for equal magnitude but opposite polarity input signals) is below 1 count. high-impedance differential inputs offer 1 pa leakage current and a 10 12 w input impedance. the 15 m v p-p noise performance guarantees a rock solid reading. the auto-zero cycle guarantees a zero display reading with a 0v input. the tc7116a and tc7117a feature a precision, low- drift internal reference, and are functionally identical to the tc7116/tc7117. a low-drift external reference is not normally required with the tc7116a/tc7117a. available packages 40-pin plastic dip 40-pin cerdip 44-pin plastic quad flat package formed leads 44-pin plastic chip carrier plcc package temperature code package range ckw 44-pin pqfp 0 c to +70 c clw 44-pin plcc 0 c to +70 c cpl 40-pin plastic dip 0 c to +70 c ijl 40-pin cerdip C 25 c to +85 c figure 1. typical tc7116/a/7/a operating circuit tc7116 tc7116a tc7117 tc7117a tc7116/a/7117/a-7 10/18/96 ordering information part code tc711x x x xxx 6 = lcd 7 = led a or blank* r (reversed pins) or blank (cpl pkg. only) * "a" parts have an improved reference tc package code (see below) : }
3-204 telcom semiconductor, inc. 3-1/2 digit analog-to-digital converters with hold tc7116 tc7116a tc7117 tc7117a absolute maximum ratings* supply voltage tc7116/tc7116a: v + to v C ................................. 15v tc7117/tc7117a: v + to gnd ............................. +6v v C to gnd ............................ C 9v analog input voltage (either input) (note 1) ........ v + to v C reference input voltage (either input) ................. v + to v C clock input tc7116/tc7116a ..................................... test to v + tc7117/tc7117a ...................................... gnd to v + package power dissipation, t a 70 c (note 2) cerdip ..............................................................2.29w plastic dip ........................................................1.23w plastic chip carrier (plcc) ..............................1.23w plastic quad flat package (pqfp) ..................1.00w operating temperature c device .............................................. 0 c to +70 c i device .......................................... C 25 c to +85 c storage temperature ............................ C 65 c to +150 c lead temperature (soldering, 10 sec) ................. +300 c *static-sensitive device. unused devices must be stored in conductive material. protect devices from static discharge and static fields. stresses above those listed under absolute maximum ratings may cause perma- nent 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 operational sections of the specifications is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. electrical characteristics (note 3) parameter test conditions min typ max unit zero input reading v in = 0v 0 digital full scale = 200 mv reading ratiometric reading v in = v ref 999 999/1000 1000 digital v ref = 100 mv reading roll-over error (difference in Cv in = +v in @ 200 mv or ? 2v C 1 0.2 +1 counts reading for equal positive and negative readings near full scale) linearity (maximum deviation from full scale = 200 mv or 2v C 1 0.2 +1 counts best straight line fit) common-mode rejection ratio (note 4) v cm = 1v, v in = 0v 50 m v/v full scale = 200 mv noise (peak-to-peak value not v in = 0v 15 m v exceeded 95% of time) full scale = 200 mv leakage current at input v in = 0v 1 10 pa zero reading drift v in = 0v c device: 0 c to +70 c 0.2 1 m v/ c i device: C25 c to +85 c12 m v/ c scale factor temperature coefficient v in = 199 mv c device: 0 c to +70 c 1 5 ppm/ c (ext ref = 0 ppm/ c) i device: C25 c to +85 c 20 ppm/ c input resistance, pin 1 note 6 30 70 k w v il , pin 1 tc7116/a only test +1.5 v v il , pin 1 tc7117/a only gnd +1.5 v v ih , pin 1 both v + C 1.5 v supply current (does not include v in = 0v 0.8 1.8 ma led current for 7117/a) analog common voltage 25 k w between common 2.4 3.05 3.35 v (with respect to positive supply) and positive supply temperature coefficient of analog common "c" device: 0 c to +70 c (with respect to positive supply) tc7116a/tc7117a 20 50 ppm/ c tc7116/tc7117 80 ppm/ c
3-205 telcom semiconductor, inc. 7 6 5 4 3 1 2 8 3-1/2 digit analog-to-digital converters with hold tc7116 tc7116a tc7117 tc7117a electrical characteristics (cont.) parameter test conditions min typ max unit temperature coefficient of analog common "i" device: C25 c to +85 c 75 ppm/ c (with respect to positive supply) 25 k w between common and positive supply (tc7116a/tc7117a) tc7116/tc7116a only peak-to-peak v + to v C = 9v 4 5 6 v segment drive voltage (note 5) tc7116/tc7116a only peak-to-peak v + to v C = 9v 4 5 6 v backplane drive voltage (note 5) tc7117/tc7117a only segment v + = 5v 5 8 ma sinking current (except pin 19) segment voltage = 3v tc7117/tc7117a only segment v + = 5v 10 16 ma sinking current (pin 19 only) segment voltage = 3v notes: 1. input voltages may exceed supply voltages, provided input current is limited to 100 m a. 2. dissipation rating assumes device is mounted with all leads soldered to printed circuit board. 3. unless otherwise noted, specifications apply at t a = +25 c, f clock = 48 khz. tc7116/tc7116a and tc7117/tc7117a are tested in the circuit of figure 1. 4. refer to "differential input" discussion. 5. backplane drive is in-phase with segment drive for off segment, 180 out-of-phase for on segment. frequency is 20 times conversion rate. average dc component is less than 50 mv. 6. the tc7116/tc7116a logic inputs have an internal pull-down resistor connected from hldr, pin 1 to test, pin 37. the tc7117/tc7117a logic inputs have an internal pull-down resistor connected from hldr, pin 1 to gnd, pin 21.
3-206 telcom semiconductor, inc. tc7116 tc7116a tc7117 tc7117a bp/ gnd 33 34 35 36 37 38 39 13 10 9 8 7 common v + 18 19 20 21 23 24 3 ab 4 pol nc in hi nc in lo b 6543 144 2 a osc 22 43 osc 42 osc 41 test 40 ref hi 25 26 27 28 f e g a c g 32 14 a/z 2 31 15 buff 2 30 16 int e 29 17 d nc 11 12 nc c d 3 2 f a 2 2 2 b 3 3 3 3 3 2 tc7116clw tc7116aclw tc7117clw tc7117aclw (plcc) 1 2 3 v c ref c ref 1 b 1 c 1 d 1 f 1 g 1 e 1 bp/ gnd 27 28 29 30 31 32 33 7 4 3 2 1 nc tc7116ckw tc7116ackw tc7117ckw tc7117ackw 12 13 14 15 17 18 g 44 43 42 41 39 38 40 ref hi common 16 37 a/z 36 buff 35 int 34 v 19 20 21 22 d 26 8 25 9 24 10 23 11 in hi 5 6 c osc test nc nc hldr 3 3 d 2 c 2 b 2 a 2 f 2 e 2 nc osc 2 osc 1 v + ref c ref c in lo 2 3 a 3 g 3 pol ab 4 e 3 f 3 b 3 (flat package) d 1 c 1 b 1 a 1 f 1 g 1 e 1 tc7116ipl tc7116aipl tc7117cpl tc7117acpl (pdip) 1 2 3 4 osc 1 5 6 7 8 9 10 11 12 test v common c az hldr d 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 2 c 2 b 2 a 2 f 2 e 2 d 3 b 3 f 3 e 3 ab 4 (minus sign) 10's 100's 1000's (tc7116/7117) (tc7116a/tc7117a) 100's osc 2 osc 3 + ref v+ c + ref c ref v + in v in v buff v int v g c a g bp/gnd pol 3 3 3 2 d 1 c 1 b 1 a 1 f 1 g 1 e 1 1's notes: 1. nc = no internal connection. 2. pins 9, 25, 40, and 56 are connected to the die substrate. the potential at these pins is approximately v . no external con nections should be made. + + + hldr tc7116ijl tc7116aijl tc7117ijl tc7117aijl (cerdip) 1 2 3 4 osc 1 5 6 7 8 9 10 11 12 test v common c az hldr d 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 2 c 2 b 2 a 2 f 2 e 2 d 3 b 3 f 3 e 3 ab 4 (minus sign) 10's 100's 1000's (tc7116/7117) (tc7116a/tc7117a) 100's osc 2 osc 3 + ref v+ c + ref c ref v + in v in v buff v int v g c a g bp/gnd pol 3 3 3 2 d 1 c 1 b 1 a 1 f 1 g 1 e 1 1's pin configurations 3-1/2 digit analog-to-digital converters with hold
3-207 telcom semiconductor, inc. 7 6 5 4 3 1 2 8 pin description 40-pin pdip/ 44-pin 40-pincerdip plastic quad pin number flat package normal pin number symbol description 1 8 hldr hold pin, logic 1 holds present display reading. 29d 1 activates the d section of the units display. 310c 1 activates the c section of the units display. 411b 1 activates the b section of the units display. 512a 1 activates the a section of the units display. 613f 1 activates the f section of the units display. 714g 1 activates the g section of the units display. 815e 1 activates the e section of the units display. 916d 2 activates the d section of the tens display. 10 17 c 2 activates the c section of the tens display. 11 18 b 2 activates the b section of the tens display. 12 19 a 2 activates the a section of the tens display. 13 20 f 2 activates the f section of the tens display. 14 21 e 2 activates the e section of the tens display. 15 22 d 3 activates the d section of the hundreds display. 16 23 b 3 activates the b section of the hundreds display. 17 24 f 3 activates the f section of the hundreds display. 18 25 e 3 activates the e section of the hundreds display. 19 26 ab 4 activates both halves of the 1 in the thousands display. 20 27 pol activates the negative polarity display. 21 28 bp lcd backplane drive output (tc7116/tc7116a). gnd digital ground (tc7117/tc7117a). 22 29 g 3 activates the g section of the hundreds display. 23 30 a 3 activates the a section of the hundreds display. 24 31 c 3 activates the c section of the hundreds display. 25 32 g 2 activates the g section of the tens display. 26 34 v C negative power supply voltage. 27 35 v int integrator output. connection point for integration capacitor. see integration capacitor section for additional details. 28 36 v buff integration resistor connection. use a 47 k w resis tor for 200 mv full-scale range and a 470 k w resistor for 2v full-scale range. 29 37 c az the size of the auto-zero capacitor influences system noise. use a 0.47 m f capacitor for 200 mv full scale and a 0.047 m f capacitor for 2v full scale. see auto-zero capacitor paragraph for more details. 30 38 v C in the analog low input is connected to this pin. 31 39 v + in the analog high input is connected to this pin. 39 40 common this pin is primarily used to set the analog common- mode common voltage for battery operation or in systems where the input signal is referenced to the power supply. see analog common paragraph for more details. it also acts as a reference voltage source. tc7116 tc7116a tc7117 tc7117a 3-1/2 digit analog-to-digital converters with hold
3-208 telcom semiconductor, inc. tc7116 tc7116a tc7117 tc7117a pin description (cont.) 40-pin cerdip 44-pin 40-pin pdip plastic quad pin number flat package normal pin number symbol description 33 41 c C ref see pin 34. 34 42 c + ref a 0.1 m f capacitor is used in most applications. if a large, common-mode voltage exists (e.g., the v in C pin is not at analog common), and a 200 mv scale is used, a 1 m f capacitor is recommended and will hold the roll-over error to 0.5 count. 35 43 v + positive power supply voltage. 36 44 v + ref the analog input required to generate a full-scale output (1999 counts). place 100 mv between pins 32 and 36 for 199.9 mv full scale. place 1v between pins 32 and 36 for 2v full scale. see paragraph on reference voltage. 37 3 test lamp test. when pulled high (to v + ), all segments will be turned on and the display should read C1888. it may also be used as a negative supply for externally- generated decimal points. see test paragraph for more details. 38 4 osc 3 see pin 40. 39 6 osc 2 see pin 40. 40 7 osc 1 pins 40, 39 and 38 make up the oscillator section. for a 48 khz clock (3 readings per sec), connect pin 40 to the junction of a 100 k w resistor and a 100 pf capacitor. the 100 k w resistor is tied to pin 39 and the 100 pf capacitor is tied to pin 38. 3-1/2 digit analog-to-digital converters with hold
3-209 telcom semiconductor, inc. 7 6 5 4 3 1 2 8 reference integrate phase the final phase is reference integrate, or deintegrate. input low is internally connected to analog common and input high is connected across the previously charged reference 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 proportional to the input signal. the digital reading displayed is: tc7116 tc7116a tc7117 tc7117a c ref c ref buff c ref r int v + c az auto- zero v int 28 35 29 27 33 36 34 10 ? 31 a/z a/z int a/z & de (? 32 30 int 26 integrator v + ?v comparator to digital section de (+) de (? de (+) de (? v + a/z analog common + v in + v in v c int v ref + low temp drift zener v ref v + + + + analog section (all pin designations refers to 40-pin dip) figure 3 shows the block diagram of the analog section for the tc7116/tc7116a and tc7117/tc7117a. each measurement cycle is divided into three phases: (1) auto- zero (a-z), (2) signal integrate (int), and (3) reference integrate (ref) or deintegrate (de). auto-zero phase high and low inputs are disconnected from the pins and internally shorted to analog common. the reference capacitor is charged to the reference voltage. a feedback loop is closed around the system to charge the auto-zero capacitor (c az ) to compensate for offset voltages in the buffer amplifier, integrator, and comparator. since the com- parator is included in the loop, a-z accuracy is limited only by system noise. the offset referred to the input is less than 10 m v. signal-integrate phase the auto-zero loop is opened, the internal short is removed, and the internal high and low inputs are con- nected to the external pins. the converter then integrates the differential voltages between v + in and v C in for a fixed time. this differential voltage can be within a wide com- mon-mode range; 1v of either supply. however, if the input signal has no return with respect to the converter power supply, v C in can be tied to analog common to establish the correct common-mode voltage. at the end of this phase, the polarity of the integrated signal is determined. figure 3. analog section of tc7116/tc7116a and tc7117/tc7117a 1000 . v in v ref reference the positive reference voltage (v + ref ) is referred to analog common. differential input this input can accept differential voltages anywhere within the common-mode range of the input amplifier or, specifically, from 1v below the positive supply to 1v above the negative supply. in this range, the system has a cmrr of 86 db, typical. however, since the integrator also swings with the common-mode voltage, care must be exercised to ensure that the integrator output does not saturate. a worst- case condition would be a large, positive common- mode voltage with a near full-scale negative differential input voltage. the negative-input signal drives the integra- tor positive when most of its swing has been used up by the positive common-mode voltage. for these critical applica- tions, the integrator swing can be reduced to less than the tc7116 tc7116a tc7117 tc7117a 3-1/2 digit analog-to-digital converters with hold
3-210 telcom semiconductor, inc. tc7116 tc7116a bp test 37 21 v + v + gnd to lcd decimal point to lcd back- plane 4049 v + ref v + 1.2v ref common tc7116 tc7116a tc7117 tc7117a 6.8 k w v + tc9491czm w 20 k figure 4. using an external reference recommended 2v full-scale swing with little loss of accu- racy. the integrator output can swing within 0.3v of either supply without loss of linearity. analog common this pin is included primarily to set the common-mode voltage for battery operation (tc7116/tc7116a) or for any system where the input signals are floating with respect to the power supply. the analog common pin sets a voltage approximately 2.8v more negative than the positive supply. this is selected to give a minimum end-of-life battery voltage of about 6v. however, analog common has some attributes of a reference voltage. when the total supply voltage is large enough to cause the zener to regulate (>7v), the analog common voltage will have a low voltage coefficient (0.001%/ %), low output impedance ( @ 15 w ), and a temperature coef- ficient of less than 20 ppm/ c, typically, and 50 ppm maxi- mum. the tc7116/tc7117 temperature coefficients are typically 80 ppm/ c. an external reference may be used, if necessary, as shown in figure 4. analog common is also used as v C in return during auto- zero and deintegrate. if v C in is different from analog common, a common-mode voltage exists in the system and is taken care of by the excellent cmrr of the converter. however, in some applications, v C in will be set at a fixed, known voltage (power supply common for instance). in this application, analog common should be tied to the same point, thus removing the common-mode voltage from the converter. the same holds true for the reference voltage; if it can be conveniently referenced to analog common, it should be. this removes the common-mode voltage from the reference system. within the ic, analog common is tied to an n-channel fet that can sink 30 ma or more of current to hold the voltage 3v below the positive supply (when a load is trying to pull the analog common line positive). however, there is only 10 m a of source current, so analog common may easily be tied to a more negative voltage, thus overriding the internal reference. test the test pin serves two functions. on the tc7117/ tc7117a, it is coupled to the internally-generated digital supply through a 500 w resistor. thus, it can be used as a figure 7. clock circuits tc7116/tc7116a tc7117/tc7117a to counter crystal rc network 40 38 ext osc 39 to test pin on tc7116/tc7116a to ground pin on tc7117/tc7117a figure 6. exclusive ?r?gate for decimal point drive tc7116 tc7116a decimal point select v + v + test gnd 4030 to lcd decimal points bp figure 5. simple inverter for fixed decimal point 3-1/2 digit analog-to-digital converters with hold tc7116 tc7116a tc7117 tc7117a
3-211 telcom semiconductor, inc. 7 6 5 4 3 1 2 8 negative supply for externally-generated segment drivers, such as decimal points or any other presentation the user may want to include on the lcd. (figures 5 and 6 show such an application.) no more than a 1 ma load should be applied. the second function is a "lamp test." when test is pulled high (to v + ), all segments will be turned on and the display should read C1888. the test pin will sink about 10 ma under these conditions. digital section figures 8 and 9 show the digital section for tc7116/ tc7116a and tc7117/tc7117a, respectively. for the tc7116/tc7116a (figure 8), an internal digital ground is generated from a 6v zener diode and a large p-channel source follower. this supply is made stiff to absorb the relative large capacitive currents when the backplane (bp) voltage is switched. the bp frequency is the clock fre- quency 4 800. for 3 readings per second, this is a 60-hz square wave with a nominal amplitude of 5v. the seg- ments are driven at the same frequency and amplitude, and are in-phase with bp when off, but out-of-phase when on. in all cases, negligible dc voltage exists across the segments. figure 9 is the digital section of the tc7117/tc7117a. it is identical to the tc7116/tc7116a, except that the regulated supply and bp drive have been eliminated, and the segment drive is typically 8 ma. the 1000's output (pin 19) sinks current from two led segments, and has a 16-ma drive capability. the tc7117/tc7117a are designed to drive common anode led displays. in both devices, the polarity indication is on for analog inputs. if v C in and v + in are reversed, this indication can be reversed also, if desired. figure 8. tc7116/tc7116a digital section tc7116 tc7116a lcd phase driver thousands hundreds tens units 4 backplane 21 39 37 osc internal digital ground v + v test 6.2v 500 w 26 35 to switch drivers from comparator output clock v th = 1v 7-segment decode 7-segment decode 7-segment decode 200 40 38 typical segment output internal digital ground segment output v + 0.5 ma 2 ma latch 2 osc 3 osc 1 hldr ; 70 k w logic control 1 3-1/2 digit analog-to-digital converters with hold tc7116 tc7116a tc7117 tc7117a
3-212 telcom semiconductor, inc. 3-1/2 digit analog-to-digital converters with hold tc7116 tc7116a tc7117 tc7117a tc7117 tc7117a thousands hundreds tens units 4 39 osc v digital gnd test 35 to switch drivers from comparator output clock 7-segment decode 7-segment decode 7-segment decode 40 38 2 osc 3 osc 1 hldr control logic typical segment output digital ground to segment v + 0.5 ma 8 ma 37 21 500 w v + 1 latch ~70 k w + system timing the clocking method used for the tc7116/tc7116a and tc7117/tc7117a is shown in figure 9. three clocking methods may be used: (1) an external oscillator connected to pin 40. (2) a crystal between pins 39 and 40. (3) an rc network using all three pins. the oscillator frequency is 4 4 before it clocks the decade counters. it is then further divided to form the three convert-cycle phases: signal integrate (1000 counts), refer- ence deintegrate (0 to 2000 counts), and auto-zero (1000 to 3000 counts). for signals less than full scale, auto-zero gets the unused portion of reference deintegrate. this makes a complete measure cycle of 4000 (16,000 clock pulses) independent of input voltage. for 3 readings per second, an oscillator frequency of 48 khz would be used. to achieve maximum rejection of 60-hz pickup, the signal-integrate cycle should be a multiple of 60 hz. oscil- lator frequencies of 240 khz, 120 khz, 80 khz, 60 khz, 48 khz, 40 khz, etc. should be selected. for 50 hz rejection, oscillator frequencies of 200 khz, 100 khz, 66-2/3 khz, 50 khz, 40 khz, etc. would be suitable. note that 40 khz (2.5 readings per second) will reject both 50 hz and 60 hz. hold reading input when hldr is at a logic high the latch will not be updated. analog-to-digital conversions will continue but will not be updated until hldr is returned to low. to continu- ously update the display, connect to test (tc7116/tc7116a) or ground (tc7117/tc7117a), or disconnect. this input is cmos compatible with 70 k w typical resistance to test (tc7116/tc7116a) or ground (tc7117/tc7117a). figure 9. tc7117/tc7117a digital section
3-213 telcom semiconductor, inc. 7 6 5 4 3 1 2 8 3-1/2 digit analog-to-digital converters with hold tc7116 tc7116a tc7117 tc7117a component value selection auto-zero capacitor the size of the auto-zero capacitor has some influ- ence on system noise. for 200 mv full scale, where noise is very important, a 0.47 m f capacitor is recommended. on the 2v scale, a 0.047 m f capacitor increases the speed of recovery from overload and is adequate for noise on this scale. reference capacitor a 0.1 m f capacitor is acceptable in most applications. however, where a large common-mode voltage exists (i.e., the v C in pin is not at analog common), and a 200-mv scale is used, a larger value is required to prevent roll-over error. generally, 1 m f will hold the roll-over error to 0.5 count in this instance. integrating capacitor the integrating capacitor should be selected to give the maximum voltage swing that ensures tolerance build-up will not saturate the integrator swing (approximately 0.3v from either supply). in the tc7116/tc7116a or the tc7117/ tc7117a, when the analog common is used as a reference, a nominal 2v full- scale integrator swing is acceptable. for the tc7117/tc7117a, with 5v supplies and analog com- mon tied to supply ground, a 3.5v to 4v swing is nominal. for 3 readings per second (48 khz clock), nominal values for c int are 0.22 m 1f and 0.10 m f, respectively. if different oscillator frequencies are used, these values should be changed in inverse proportion to maintain the output swing. the integrating capacitor must have low dielectric ab- sorption to prevent roll-over errors. polypropylene capaci- tors are recommended for this application. integrating resistor both the buffer amplifier and the integrator have a class a output stage with 100 m a of quiescent current. they can supply 20 m a of drive current with negligible nonlinearity. the integrating resistor should be large enough to remain in this very linear region over the input voltage range, but small enough that undue leakage requirements are not placed on the pc board. for 2v full scale, 470 k w is near optimum and, similarly, 47 k w for 200 mv full scale. oscillator components for all frequency ranges, a 100-k w resistor is recom- mended; the capacitor is selected from the equation: for a 48 khz clock (3 readings per second), c = 100 pf. figure 10. negative power supply generation with tc7660 v ref + v + tc7117 tc7117a 36 10 f v in + v in com gnd 32 31 30 21 10 f v in v (?v) 5 3 8 2 4 +5v 35 tc7660 26 + + + tc04 led drive reference voltage to generate full-scale output (2000 counts), the analog input requirement is v in = 2 v ref . thus, for the 200 mv and 2v scale, v ref should equal 100 mv and 1v, respectively. in many applications, where the adc is connected to a transducer, a scale factor exists between the input voltage and the digital reading. for instance, in a measuring system the designer might like to have a full-scale reading when the voltage from the transducer is 700 mv. instead of dividing the input down to 200 mv, the designer should use the input voltage directly and select v ref = 350 mv. suitable values for integrating resistor and capacitor would be 120 k w and 0.22 m f. this makes the system slightly quieter and also avoids a divider network on the input. the tc7117/tc7117a, with 5v supplies, can accept input signals up to 4v. another advantage of this system is when a digital reading of zero is desired for v in 1 0. temperature and weighing systems with a variable tare are examples. this offset reading can be conveniently generated by connecting the voltage transducer between v + in and analog common, and the variable (or fixed) offset voltage between analog com- mon and v C in . tc7117/tc7117a power supplies the tc7117/tc7117a are designed to operate from 5v supplies. however, if a negative supply is not available, it can be generated with a tc7660 dc-to-dc converter and two capacitors. figure 10 shows this application. in selected applications, a negative supply is not re- quired. the conditions for using a single +5v supply are: (1) the input signal can be referenced to the center of the common-mode range of the converter. (2) the signal is less than 1.5v. (3) an external reference is used. 45 rc f = .
3-214 telcom semiconductor, inc. 3-1/2 digit analog-to-digital converters with hold tc7116 tc7116a tc7117 tc7117a typical applications figure 13. circuit for developing underrange and overrange signals from tc7116/tc7116a outputs figure 12. tc7117/tc7117a internal reference (200 mv full scale, 3 rps, v C in tied to gnd for single-ended inputs.) 100 k w 100 pf 0.47 ? 47 k w 0.22 ? to display to backplane 0.1 pf 21 1 k w 22 k w 9v set v ref = 100 mv tc7116 tc7116a 0.01 ? + in 1 m w 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 + 21 20 40 35 26 to logic gnd v to logic v cc + v cd4077 u/r o/r cd4023 or 74c10 tc7116 tc7116a o/r = overrange u/r = underrange 100 pf 0.47 ? 47 k w to display 0.1 pf 1 k w w v set v ref = 100 mv + 10 k 10 k w 1.2v 0.01 ? in 1 m w + 100 k w v 0.22 ? 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 tc9491czm tc7117 tc7117a 100 k w 100 pf 0.47 ? 47 k w 0.22 ? to display 0.1 pf 21 1 k w 22 k w set v ref = 100 mv 0.01 ? + in 1 m w 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 ?v +5v tc7117 tc7117a figure 11. tc7116/tc7116a using the internal reference (200 mv full scale, 3 readings per second (rps) figure 14. tc7117/tc7117a with a 1.2v external band-gap reference (v C in tied to common)
3-215 telcom semiconductor, inc. 7 6 5 4 3 1 2 8 3-1/2 digit analog-to-digital converters with hold tc7116 tc7116a tc7117 tc7117a applications information the tc7117/tc7117a sink the led display current, causing heat to build up in the ic package. if the internal voltage reference is used, the changing chip temperature can cause the display to change reading. by reducing the led common anode voltage, the tc7117/tc7117a pack- age power dissipation is reduced. figure 17 is a curve-tracer display showing the relation- ship between output current and output voltage for typical tc7117cpl/tc7117acpl devices. since a typical led has 1.8v across it at 8 ma and its common anode is connected to +5v, the tc7117/tc7117a output is at 3.2v (point a, figure 17). maximum power dissipation is 8.1 ma 3.2v 24 segments = 622 mw. however, notice that once the tc7117/tc7117a's out- put voltage is above 2v, the led current is essentially constant as output voltage increases. reducing the output voltage by 0.7v (point b figure 17) results in 7.7 ma of led current, only a 5% reduction. maximum power dissipation is now only 7.7 ma 2.5v 24 = 462 mw, a reduction of 26%. an output voltage reduction of 1v (point c) reduces led current by 10% (7.3 ma), but power dissipation by 38% (7.3 ma 2.2v 24 = 385 mw). reduced power dissipation is very easy to obtain. figure 18 shows two ways: either a 5.1 w , 1/4w resistor, or a 1a diode placed in series with the display (but not in series with the tc7117/tc7117a). the resistor reduces the tc7117/tc7117a's output voltage (when all 24 segments are on) to point c of figure 17. when segments turn off, the output voltage will increase. the diode, however, will result in a relatively steady output voltage, around point b. in addition to limiting maximum power dissipation, the resistor reduces change in power dissipation as the display changes. the effect is caused by the fact that, as fewer segments are on, each on output drops more voltage and current. for the best case of six segments (a 111 display) to worst case (a 1888 display), the resistor circuit will change about 230 mw, while a circuit without the resistor will change about 470 mw. therefore, the resistor will reduce the effect of display dissipation on reference voltage drift by about 50%. the change in led brightness caused by the resistor is almost unnoticeable as more segments turn off. if display brightness remaining steady is very important to the de- signer, a diode may be used instead of the resistor. figure 15. recommended component values for 2v full scale (tc7116/tc7116a and tc7117/tc7117a) figure 16. tc7117/tc7117a operated from single +5v supply (an external reference must be used in this application.) 100 k w 100 pf 0.047 ? 470 k w 0.22 ? to display 0.1 ? 25 k w 24 k v + set v ref = 1v 0.01 ? + in 1m w v 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 tc7116 tc7116a tc7117 tc7117a w 100 pf 0.47 ? 47 k w to display 0.1 pf 1 k w w v set v ref = 100 mv + 10 k 10 k w 1.2v 0.01 ? in 1 m w + 100 k w 0.22 ? 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 tc9491czm tc7117 tc7117a
3-216 telcom semiconductor, inc. 3-1/2 digit analog-to-digital converters with hold tc7116 tc7116a tc7117 tc7117a tp2 tp5 100 k w tp1 24 k w 1 k w 0.1 ? tp3 0.01 ? + in 0.22 ? display display 100 pf +5v w 1 m ?v w 150 k 0.47 ? tc7117 tc7117a 40 tp 4 30 35 21 20 10 1 47 k w 1n4001 1.5 w , 1/4w figure 18. diode or resistor limits package power dissipation figure 17. tc7117/tc7117a output current vs output voltage

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