where NB represents the digital input word. Since

AGND is common to all four DACs, all outputs will be

more than +1V above DGND, or more than 2.5V below

DGND.

Figures 14 and 15 illustrate the generation of negative

offsets with bipolar outputs. In these circuits, AGND is

biased negatively (up to -2.5V with respect to DGND) to

provide an arbitrary negative output voltage for a 0

input code. The output voltage at OUTA is:

OUTA = -(R2/R1)(2.5V) + (NB/256)(2.5V)(R2/R1+1)

where NB represents the digital input word. Since

AGND is common to all four DACs, all outputs will be

for Figure 14 and 15's circuits with R1 = R2. The

ICL7612 op amp is chosen because its common-mode

range extends to both supply rails.

Quad, Serial 8-Bit DACs

with Rail-to-Rail Outputs

16

______________________________________________________________________________________

Figure 11. MAX509 Unipolar Output Circuit

REFD

DAC A

DAC B

DAC C

DAC D

REFC

REFB

REFA

MAX509

OUTA

OUTB

OUTC

OUTD

SERIAL

INTERFACE

NOT SHOWN

2

1

20

19

+5V

16

517

418

3

-5V (OR GND)

68

AGND

DGND

Figure 12. MAX510 Unipolar Output Circuit

DAC A

DAC B

DAC C

DAC D

REFAB

MAX510

OUTA

OUTB

OUTC

OUTD

SERIAL

INTERFACE

NOT SHOWN

2

1

16

15

+5V

414

3

-5V (OR GND)

56

AGND

DGND

REFCD

13

Figure 13. MAX509/MAX510 AGND Bias Circuits (Positive

Offset)

DAC A

MAX509

5

18

AGND

2

OUTA

DGND

REFA

3

8

6

+5V

-5V (OR GND)

DAC A

MAX510

4

14

AGND

2

OUTA

DGND

REFAB

3

6

5

+5V

-5V (OR GND)

SERIAL INTERFACE NOT SHOWN