DAC0830/DAC0831/DAC0832 8-Bit MuP Compatible, Double ...

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DAC0830 Series Application Hints (Continued)t sOP Amp C C (O to Full Scale)LF356 22 pF 4 msLF351 22 pF 5 msLF357 10 pF 2 msFIGURE 824 kX RESISTOR ADDED FROMbINPUT TOGROUND TO INSURE STABILITYV OUT eV REF(DIGITAL CODEb128)1281 LSBe l V REFl128TLH5608–10Input CodeIDEAL V OUTMSB LSB aV REF bV REFTHESE RESISTORS ARE AVAILABLE FROM 1 1 1 1 1 1 1 1 V REF b1 LSB blV REFla1 LSBBECKMAN INSTRUMENTS INC AS THEIR1 1 0 0 0 0 0 0 V REF 2 blVPART NO 694-3-R10K-DREFl21 0 0 0 0 0 0 0 0 00 1 1 1 1 1 1 1 l b1 LSB a1 LSBV0 0 1 1 1 1 1 1 b REFlb1 l VLSB REFla1 LSB220 0 0 0 0 0 0 0 blV REFl alV REFlFIGURE 926 Full-Scale AdjustmentIn the case where the matching of R fb to the R value of theR-2R ladder (typically g02%) is insufficient for full-scaleaccuracy in a particular application the V REF voltage can beadjusted or an external resistor and potentiometer can beadded as shown in Figure 10 to provide a full-scale adjustmentThe temperature coefficients of the resistors used for thisadjustment are an important concern To prevent degradationof the gain error temperature coefficient by the externalresistors their temperature coefficients ideally would haveto match that of the internal DAC resistors which is a highlyimpractical constraint For the values shown in Figure 10 ifthe resistor and the potentiometer each had a temperaturecoefficient of g100 ppmC maximum the overall gain errortemperature coefficent would be degraded a maximum of00025%C for an adjustment pot setting of less than 3%of R fb 27 Using the DAC0830 in a Voltage SwitchingConfigurationThe R-2R ladder can also be operated as a voltage switchingnetwork In this mode the ladder is used in an invertedmanner from the standard current switching configurationThe reference voltage is connected to one of the currentoutput terminals (I OUT1 for true binary digital control I OUT2is for complementary binary) and the output voltage is takenfrom the normal V REF pin The converter output is now avoltage in the range from 0V to 255256 V REF as a functionof the applied digital code as shown in Figure 11TLH5608–11FIGURE 10 Adding Full-Scale Adjustment12
DAC0830 Series Application Hints (Continued)FIGURE 11 Voltage Mode SwitchingTLH5608–12This configuration offers several useful application advantagesSince the output is a voltage an external op amp isnot necessarily required but the output impedance of theDAC is fairly high (equal to the specified reference inputresistance of 10 kX to 20 kX) so an op amp may be usedfor buffering purposes Some of the advantages of thismode are illustrated in Figures 12 13 14 and 15There are two important things to keep in mind when usingthis DAC in the voltage switching mode The applied referencevoltage must be positive since there are internal parasiticdiodes from ground to the I OUT1 and I OUT2 terminalswhich would turn on if the applied reference went negativeThere is also a dependence of conversion linearity andgain error on the voltage difference between V CC and thevoltage applied to the normal current output terminals Thisis a result of the voltage drive requirements of the ladderswitches To ensure that all 8 switches turn on sufficiently(so as not to add significant resistance to any leg of theladder and thereby introduce additional linearity and gainerrors) it is recommended that the applied reference voltagebe kept less than a5V DC and V CC be at least 9V morepositive than V REF These restrictions ensure less than01% linearity and gain error change Figures 16 17 and 18characterize the effects of bringing V REF and V CC closertogether as well as typical temperature performance of thisvoltage switching configuration Voltage switching mode eliminates output signal inversion and therefore aneed for a negative power supply Zero code output voltage is limited by the low level output saturation voltageof the op amp The 2 kX pull-down resistor helps to reduce this voltage V OS of the op amp has no effect on DAC linearityFIGURE 12 Single Supply DAC V OUT e25V D128 b1 JTLH5608–13 Slewing and settling time for a full scale output change is 18 msFIGURE 13 Obtaining a Bipolar Output from a FixedReference with a Single Op Amp13
Page 1: DAC0830DAC0831DAC0832 8-Bit mPCompa
Page 6 and 7: Linearity Errora) End point test af
Page 8 and 9: DAC0830 Series Application Hints (C
Page 16 and 17: Applications (Continued)Variable f
Page 18 and 19: Ordering InformationTemperature Ran
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DAC0830/DAC0831/DAC0832 8-Bit MuP Compatible, Double ...

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