REV.

AD7226

–9–

DAC A

DAC B

DAC C

DAC D

MSB

DGND

AGND

WR

A1

A0

LSB

DB7

DB0

Figure 8. AD7226 Unipolar Output Circuit

Table II. Unipolar Code Table

DAC Latch Contents

MSB

LSB

Analog Output

1 1 1 1

1 1 1 1

+

Ê

ËÁ

ˆ

¯˜

255

256

1 0 0 0

0 0 0 1

+

Ê

ËÁ

ˆ

¯˜

129

256

1 0 0 0

0 0 0 0

+

Ê

ËÁ

ˆ

¯˜ =+

V

V

REF

REF

128

256

2

0 1 1 1

1 1 1 1

+

Ê

ËÁ

ˆ

¯˜

127

256

0 0 0 0

0 0 0 1

+

Ê

ËÁ

ˆ

¯˜

1

256

0 0 0 0

0 0 0 0

0 V

Note LSB

V

V

REF

REF

:

–

=

()

ËÁ

ˆ

¯˜

2

1

256

8

(2)

Bipolar Output Operation

Each of the DACs of the AD7226 can be individually config-

ured to provide bipolar output operation. This is possible using

one external amplifier and two resistors per channel. Figure 9

shows a circuit used to implement offset binary coding (bipolar

operation) with DAC A of the AD7226. In this case

V

R

R

DV

R

R

V

OUT

A

REF

REF

=+

Ê

ËÁ

ˆ

¯˜

¥

ËÁ

ˆ

¯˜

¥

()

1

2

1

2

1

–

(3)

With R1 = R2

VD

V

OUT

A

REF

=

21

–

(4)

Mismatch between R1 and R2 causes gain and offset errors and

therefore these resistors must match and track over tempera-

ture. Once again the AD7226 can be operated in single supply

or from positive/negative supplies. Table III shows the digital

code versus output voltage relationship for the circuit of Figure 9

with R1 = R2.

DAC A

DGND

AGND

R2

R1

+15V

–15V

R1, R2 = 10k

0.1%

*DIGITAL INPUTS OMITTED

FOR CLARITY

Figure 9. AD7226 Bipolar Output Circuit

Table III. Bipolar (Offset Binary) Code Table

DAC Latch Contents

MSB

LSB

Analog Output

1 1 1 1

1 1 1 1

+

Ê

ËÁ

ˆ

¯˜

127

128

1 0 0 0

0 0 0 1

+

Ê

ËÁ

ˆ

¯˜

1

128

1 0 0 0

0 0 0 0

0 V

0 1 1 1

1 1 1 1

1

128

Ê

ËÁ

ˆ

¯˜

0 0 0 0

0 0 0 1

127

128

Ê

ËÁ

ˆ

¯˜

0 0 0 0

0 0 0 0

––

VV

REF

REF

128

128

Ê

ËÁ

ˆ

¯˜ =

AGND BIAS

The AD7226 AGND pin can be biased above system GND

(AD7226 DGND) to provide an offset “zero” analog output

voltage level. Figure 10 shows a circuit configuration to achieve

can be expressed as:

VA

V

D V

OUT

BIAS

A

IN

=+

()

(5)

(0

£ D £ 255/256).

D