Datasheet

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
4 (I
OUT 1A
), and the normal V
REF
input pin becomes the DAC
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 V
REF
255
256




, +1.4941 V
1 0 0 0 0 0 0 1 V
REF
129
256




, +0.7559 V
1 0 0 0 0 0 0 0 V
REF
128
256




, +0.7500 V
0 1 1 1 1 1 1 1 V
REF
127
256




, +0.7441 V
0 0 0 0 0 0 0 1 V
REF
1
256




, +0.0059 V
0 0 0 0 0 0 0 0 V
REF
0
256




, 0.0000 V
Figure 8. Unipolar Supply, Voltage Output DAC Operation