AD7225LPZ datasheet(14/24 Pages) AD

14 / 24 page

AD7225

Rev. C | Page 14 of 24

BIPOLAR OUTPUT OPERATION

Each of the DACs of the AD7225 can be individually confi-

gured to provide bipolar output operation. This is possible

using one external amplifier and two resistors per channel.

Figure 17 shows a circuit used to implement offset binary

coding (bipolar operation) with DAC A (DAC Channel A)

of the AD7225. In this case,

(

)

(

)

REF

OUT













−











 +

With R1 = R2

(

) ( )

REF

OUT

−

where DA is a fractional representation of the digital word in

Latch A (0 ≤ DA ≤ 255/256).

Mismatch between R1 and R2 causes gain and offset errors and,

therefore, these resistors must match and track over tempera-

ture. The AD7225 can be operated in single supply or from

positive/negative supplies. Table 8 shows the digital code vs.

output voltage relationship for the circuit of Figure 17 with

R1 = R2.

+15V

–15V

VDD

VSS

AGND

DGND

VOUTA

DAC A

AD7225*

VREFA

VOUT

VREF

R1, R2 = 10k

Ω ± 0.1%.

*DIGITAL INPUTS OMITTED

FOR CLARITY.

Figure 17. Bipolar Output Circuit

Table 8. Bipolar (Offset Binary) Code Table

DAC Latch Contents

Analog Output

MSB

LSB

1111

( )

128

127

REF

1000

0001

( )

128

REF

1000

0000

0 V

0111

1111

( )

128

REF

−

0000

0001

( )

128

127

REF

−

0000

( )

REF

−

128

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