MAX509/MAX510
where NB represents the digital input word. Since
AGND is common to all four DACs, all outputs will be
offset by V
BIAS
in the same manner. Do not bias AGND
more than +1V above DGND, or more than 2.5V below
DGND.
Figures 14 and 15 illustrate the generation of negative
offsets with bipolar outputs. In these circuits, AGND is
biased negatively (up to -2.5V with respect to DGND) to
provide an arbitrary negative output voltage for a 0
input code. The output voltage at OUTA is:
OUTA = -(R2/R1)(2.5V) + (NB/256)(2.5V)(R2/R1+1)
where NB represents the digital input word. Since
AGND is common to all four DACs, all outputs will be
offset by V
BIAS
in the same manner. Table 3, with
V
REF
= 2.5V, shows the digital code vs. output voltage
for Figure 14 and 15's circuits with R1 = R2. The
ICL7612 op amp is chosen because its common-mode
range extends to both supply rails.
Quad, Serial 8-Bit DACs
with Rail-to-Rail Outputs
16 ______________________________________________________________________________________
Figure 11. MAX509 Unipolar Output Circuit
