DAC1219 datasheet(9/12 Pages) NSC

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Application Hints (Continued)

31 Zero and Full-Scale Adjustments

The three adjustments needed for this circuit are shown in

Figure 7 The first step is to set all of the digital inputs LOW

(to force IOUT1 to 0) and then trim ‘‘zero adjust’’ for zero

volts at the inverting input (pin 2) of OA1 Next with a code

of all zeros still applied adjust ‘‘- full-scale adjust’’ the refer-

ence voltage for VOUT e g

l(ideal VREF)l The sign of the

output voltage will be opposite that of the applied reference

Finally set all of the digital inputs HIGH and adjust ‘‘a full-

scale adjust’’ for VOUTeVREF (511512) The sign of the

output at this time will be the same as that of the reference

voltage This a full-scale adjustment scheme takes into ac-

count the effects of the VOS of amplifier A2 (as long as this

offset is less than 01% of VREF) and any gain errors due to

external resistor mismatch

40 MISCELLANEOUS APPLICATION HINTS

The devices are CMOS products and reasonable care

should be exercised in handling them to prevent catastroph-

ic failures due to electrostatic discharge

During power-up supply voltage sequencing the negative

supply of the output amplifier may appear first This will typi-

cally cause the output of the op amp to bias near the nega-

tive supply potential No harm is done to the DAC however

as the on-chip 15 kX feedback resistor sufficiently limits the

current flow from IOUT1 when this lead is clamped to one

diode drop below ground

As a general rule any unused digital inputs should be tied

high or low as required by the application As a trouble-

shooting aid if any digital input is left floating the DAC will

interpret that input as a logical 1 level

Additional Application Ideas

For the circuits shown D represents the decimal equivalent of the binary digital input code D ranges from 0 (for an all zeros

input code) to 4095 (for an all ones input code) and for any code can be determined from

D e 2048(A1) a 1024(A2) a 512(A2) a

2(A11) a 1(A12)

where AN e 1 if that input is high

AN e 0 if that input is low

DAC Controlled Amplifier

TLH5691 – 10

DAC1219 Datasheet(PDF) 9 Page - National Semiconductor (TI)