Rainbow Electronics MAX510 - Manual (Page 16)

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
REFD
DAC A
DAC B
DAC C
DAC D
REFC REFB REFA
MAX509
OUTA
OUTB
OUTC
OUTD
SERIAL
INTERFACE
NOT SHOWN
REFERENCE INPUTS (V SS TO V DD )
2
1
20
19
V DD
+5V
16 5 17 4 18
3
-5V (OR GND)
6 8
V SS AGND DGND
Figure 12. MAX510 Unipolar Output Circuit
DAC A
DAC B
DAC C
DAC D
REFAB
MAX510
OUTA
OUTB
OUTC
OUTD
SERIAL
INTERFACE
NOT SHOWN
REFERENCE INPUTS (V SS TO V DD )
2
1
16
15
V DD
+5V
4 14
3
-5V (OR GND)
5 6
V SS AGND DGND REFCD
13
Figure 13. MAX509/MAX510 AGND Bias Circuits (Positive
Offset)
DAC A
MAX509
5 18
AGND
2
OUTA
DGND V SS
REFA V DD
3 8
V IN
V BIAS
6
+5V
-5V (OR GND)
DAC A
MAX510
4 14
AGND
2
OUTA
DGND V SS
REFAB V DD
3 6
V IN
V BIAS
5
+5V
-5V (OR GND)
SERIAL INTERFACE NOT SHOWN