Datasheet

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APPLICATION INFORMATION
BIPOLAR OPERATION USING THE DAC8881
´V
BIP
(CODE)= 1+
R
3
R
1
V
REF
R
3
R
2
R
3
R
1
+
CODE
65536
-
´
(2)
´ R
3
R
1
=
V
REF
V
BIP
(3)
R
2
=
V
REF
´ R
3
V
BIP
V-
REF
(4)
DAC8881
R
1
R
2
V
BIP
V
REFL
V
REFH
V
REF
R
3
OPA211
V
OUT
+15V
-15V
NOTE:Somepinsomittedforclarity.
DAC8881
SBAS422A – JULY 2007 – REVISED SEPTEMBER 2007
The DAC8881 is designed for single-supply operation; however, a bipolar output range is also possible using the
circuit shown in Figure 72 . This circuit gives a bipolar output voltage range of V
BIP
, where V
BIP
is represented by
Equation 2 . Note that for this circuit to work, the DAC8881 must operate in the gain = 1X mode configuration with
GAIN = DGND. The output voltage for any input code can be calculated with Figure 72 :
Where:
V
BIP
(CODE) = bipolar output voltage versus CODE from the OPA211 .
CODE = 0 to 65535. This is the digital code loaded to the DAC.
V
REF
= reference high voltage applied to the DAC8881.
By first choosing a value for resistor R
3
, R
1
and R
2
can be determined by Equation 3 and Equation 4 ,
respectively:
Where:
V
BIP
= peak desired output voltage for bipolar output.
V
REF
= reference high voltage applied to the DAC8881. NOTE: V
BIP
≥ V
REF
.
R
3
= OPA211 feedback resistor chosen by user.
Note that R
2
is not required in the circuit of Figure 72 for bipolar output voltage ranges equal to ± V
REF
.
Using the previous equations, and with V
REF
= 5V and R
3
set to 10k Ω , a ± 8V output span can be achieved with
R
1
calculated to be 6.25k Ω and R
2
to be 16.67k Ω .
Similarly, a near ± 15V rail-to-rail output can be achieved with R
1
calculated to be 3.33k Ω and R
2
calculated to be
5k Ω .
Figure 72. Bipolar Operation Using the DAC8881
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