MP7228
Bipolar Binary Operation
V
REF
R1
The Bipolar Mode configuration for each DAC requires one
external op-amp and two resistors per channel.
R2
V
REF
Figure 5. shows a typical Bipolar Operation circuit using the
MP7228. Table 3. shows the code relationship for the circuit of
Figure 5. assuming R1 = R2 .
V
OUT
–
+
V
OUT
–
+
DAC
AC Reference Signal
An AC signal can be applied to the reference of the MP7228
for multiplying capability within the upper (+10V) and lower
(+2V) limits of the reference voltage input, with either single or
dual supplies. This signal must be level shifted or AC coupled
with proper bias level before being applied to the reference in-
put. Figure 6. shows techniques for applying an AC signal to the
MP7228. Since all eight DACs share a common reference, they
will all share this AC modulated reference. Input frequencies up
to 50kHz will typically be distorted less than 0.1% .
V
GND
X (1+R2/R1) – V
SS
V
= D X V
X R2/R1
REF
OUT
n
REF
if R1 = R2
= V
V
OUT
X (2D – 1)
n
REF
Where D is the digital input code and can vary from 0 to 255
n
Figure 5. Bipolar Output Circuit
+15 V
+10 V
+4 V
R1
DC
Offset
C
AC
Reference
Input
+
–
+2 V
REF
V
V
DD
R2
–4 V
V
OUT
–
+
DAC
DC
= V
(+15) X R2/R1+R2
OFFSET
DD
–5 V or GND
GND
Figure 6. AC Reference Input Signal Circuit (AC Couple)
Rev. 2.00
10
EXAR [ EXAR CORPORATION ]
