Datasheet

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Bipolar Output Operation
0.1
µ
F
V
DD
+5 V
RFB
INV
AGNDF
AGNDS
DAC
DAC Latch
Input
Register
DAC8831
+V
−
V
SDI
SCLK
LDAC
V
OUT
R
FB
R
INV
V
REF
−
S V
REF
−
F
Serial Interface
and Control Logic
CS
+2.5 V
+
0.1
µ
F 10
µ
F
DGND
V
O
=
−
V
REF
to +V
REF
OPA277
OPA704
OPA727
V
OUT_BIP
+
ƪ
ǒ
V
OUT_UNI
) V
OS
Ǔ
(
2 ) RD
)
* V
REF
(
1 ) RD
)
ƫ
1 )
ǒ
2)RD
A
Ǔ
DAC8830
DAC8831
SLAS449D – FEBRUARY 2005 – REVISED SEPTEMBER 2007
With the aid of an external operational amplifier, the DAC8831 may be configured to provide a bipolar voltage
output. A typical circuit of such an operation is shown in Figure 47 . The matched bipolar offset resistors R
FB
and
R
INV
are connected to an external operational amplifier to achieve this bipolar output swing; typically, R
FB
= R
INV
= 28 k Ω .
Figure 47. Bipolar Output Mode of DAC8831
Table 2 shows the transfer function for this output operating mode. The DAC8831 also provides a set of Kelvin
connections to the analog ground and external reference inputs.
Table 2. Bipolar Code
DAC LATCH CONTENTS
MSB LSB ANALOG OUTPUT
1111 1111 1111 1111 +V
REF
× (32,767/32,768)
1000 0000 0000 0001 +V
REF
× (1/32,768)
1000 0000 0000 0000 0 V
0111 1111 1111 1111 – V
REF
× (1/32,768)
0000 0000 0000 0000 – V
REF
× (32,768/32,768) = – V
REF
Assuming a perfect reference, the worst-case output voltage may be calculated from the following equation:
Bipolar Mode Worst-Case Output
Where:
V
OS
= External operational amplifier input offset voltage
RD = R
FB
and R
IN
resistor matching error
A = Operational amplifier open-loop gain
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