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Bipolar Output Operation

0.1

µF

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

CS

+2.5 V

+

0.1

µF

10

µF

DGND

V

O = − VREF to +VREF

OPA277

OPA704

OPA727

V

OUT_BIP +

V

OUT_UNI ) VOS (2 ) RD) * VREF(1 ) RD)

1 )

2)RD

A

DAC8830-EP

DAC8831-EP

SGLS334C – AUGUST 2006 – REVISED APRIL 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 48. The matched bipolar offset resistors RFB and

RINV are connected to an external operational amplifier to achieve this bipolar output swing; typically, RFB = RINV

= 28 k

Ω.

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

Analog Output

MSB

LSB

1111 1111 1111 1111

VREF × (32,767/32,768)

1000 0000 0000 0000

VREF × (1/32,768)

0111 1111 1111 1111

0 V

0000 0000 0000 0001

–VREF × (1/32,768)

0000 0000 0000 0000

–VREF × (32,767/32,768) = –VREF

Figure 48. Bipolar Output Mode of DAC8831

Assuming a perfect reference, the worst-case output voltage may be calculated from the following equation:

Bipolar Mode Worst-Case Output

Where:

VOS = External operational amplifier input offset voltage

RD = RFB and RIN resistor matching error

A = Operational amplifier open-loop gain

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