®

12

DAC7611

As with the GND connection, VDD should be connected to

a +5V power supply plane or trace that is separate from the

connection for digital logic until they are connected at the

power entry point. In addition, the 10

µF and 0.1µF capaci-

tors shown in Figure 4 are strongly recommended and

should be installed as close to V

DD and ground as possible.

In some situations, additional bypassing may be required

such as a 100

µF electrolytic capacitor or even a “Pi” filter

made up of inductors and capacitors—all designed to essen-

tially lowpass filter the +5V supply, removing the high

frequency noise (see Figure 4).

OFFSET ERROR MEASUREMENT

As with most DACs, the DAC7611 can have an offset error

(or zero scale error) which is either negative or positive. If

the error is positive, the output voltage for an input code of

000H will be greater than 0V. If the error is negative, the

output voltage is below 0V. However, since the DAC7611 is

a single-supply device and cannot swing below ground, the

output voltage will be 0V, giving the impression that the

offset error is zero.

Since measuring the offset error on a DAC is such a

common task, a method is needed to reliably measure the

offset error of the DAC7611. This can easily be done as

shown in Figure 5. The resistor between V

OUT and a nega-

tive voltage provides the output amplifier some ability to

swing below ground.

FIGURE 4. Suggested Power and Ground Connections for a DAC7611 Sharing a +5V Supply with a Digital System.

FIGURE 5. Offset Error Measurement Circuit.

+

+5V

GND

100µF

Digital Circuits

+5V

GND

+5V

Power

Supply

Other

Analog

Components

V

DD

GND

DAC7611

+

10µF

0.1µF

Optional

1

2

3

4

8

7

6

5

V

OUT

GND

CLR

LD

V

DD

CS

CLK

SDI

DAC7611

+

0.1µF

10µF

+5V

R

i

≤ 200µA

–V