DAC8408

–12–

REV. A

SINGLE SUPPLY, VOLTAGE OUTPUT OPERATION

The DAC8408 can be connected with a single +5 V supply to

produce DAC output voltages from 0 V to +1.5 V. In Figure 8,

the DAC8408 R-2R ladder is inverted from its normal connec-

tion. A +1.500 V reference is connected to the current output pin

output. Instead of a normal current output, the R-2R ladder out-

puts a voltage. The OP-490, consisting of four precision low

power op amps that can operate its inputs and outputs to zero

volts, buffers the DAC to produce a low impedance output volt-

age from 0 V to +1.5 V full-scale. Table III shows the code table.

With the supply and reference voltages as shown, better than 1/2

LSB differential and integral nonlinearity can be expected. To

maintain this performance level, the +5 V supply must not drop

below 4.75 V. Similarly, the reference voltage must be no higher

than 1.5 V. This is because the CMOS switches require a mini-

mum level of bias in order to maintain the linearity performance.

Table III. Single Supply Binary Code Table (Refer to Figure 8)

DAC Data Input

MSB

LSB

Analog Output

1 1 1 1 1 1 1 1

255

256







1 0 0 0 0 0 0 1

129

256







1 0 0 0 0 0 0 0

128

256







0 1 1 1 1 1 1 1

127

256







0 0 0 0 0 0 0 1

1

256







0 0 0 0 0 0 0 0

0

256







Figure 8. Unipolar Supply, Voltage Output DAC Operation