DAC8420

REV. 0

–12–

single supply operation is obtained with the output load

connected to ground, so the output stage does not have to sink

current.

Like all amplifiers, the DAC8420 output buffers do generate

voltage noise, 52 nV/

√Hz typically. This is easily reduced by

adding a simple RC low-pass filter on each output.

Reference Configuration

The two reference inputs of the DAC8420 allow a great deal of

flexibility in circuit design. The user must take care, however, to

observe the minimum voltage input levels on VREFHI and

VREFLO to maintain the accuracy shown in the data sheet.

These input voltages can be set anywhere across a wide range

within the supplies, but must be a minimum of 2.5 V apart in

any case. See Figure 1. A wide output voltage range can be

obtained with

±5 V references, which can be provided by the

AD588 as shown in Figure 28. Many applications utilize the

DACs to synthesize symmetric bipolar wave forms, which

requires an accurate, low drift bipolar reference. The AD588

provides both voltages and needs no external components. Ad-

ditionally, the part is trimmed in production for 12-bit accuracy

over the full temperature range without user calibration. Per-

forming a Clear with the reset select CLSEL HIGH allows the

user to easily reset the DAC outputs to midscale, or zero volts in

these applications.

When driving the reference inputs VREFHI and VREFLO, it is

important to note that VREFHI both sinks and sources current,

and that the input currents of both are code dependent. Many

voltage reference products have limited current sinking capabil-

ity and must be buffered with an amplifier to drive VREFHI, in

order to maintain overall system accuracy. The input VREFLO,

however, has no such requirement.

–15V SUPPLY

DAC-8420

DIGITAL

CONTROL

4

9

15 16

14

12

11

10

8

2

3

6

7

1

5

DAC A

DAC B

DAC C

DAC D

VOUTA

VOUTB

VOUTC

VOUTD

DIGITAL INPUTS

GND

VREFLO

–5V

0.1µF

0.1µF

+15V SUPPLY

+5V

VREFHI

7

R5

R4

R6

6

R1

R2

R3

A2

A1

A3

A4

7

6

4

3

1

14

15

11

8

12

9

5

13

2

16

0.1µF

0.1µF

SYSTEM

GROUND

AD588

–15V

SUPPLY

+15V

SUPPLY

+5V

–5V

1µF

10

Figure 28.

±10 V Bipolar Reference Configuration Using the AD588