AD7392/AD7393

–10–

REV. A

UNIPOLAR OUTPUT OPERATION

This is the basic mode of operation for the AD7392. As shown

in Figure 29, the AD7392 has been designed to drive loads as

low as 5 k

Ω in parallel with 100 pF. The code table for this

operation is shown in Table II.

1

20

19

17, 18

0.01 F

+2.7V TO +5.5V

AGND/DGND

AD7392

0.1 F10 F

DIGITAL INTERFACE

CIRCUITRY OMITTED

FOR CLARITY

5k

100pF

REF

EXT

REF

R

Figure 29. AD7392 Unipolar Output Operation

Table II. Unipolar Code Table

Hexadecimal

Decimal

Output

Number

Number

Voltage (V)

in DAC Register

in DAC Register

FFF

4095

2.4994

801

2049

1.2506

800

2048

1.2500

7FF

2047

1.2494

000

0

0

The circuit can be configured with an external reference plus

power supply or powered from a single dedicated regulator

or reference depending on the application performance re-

quirements.

BIPOLAR OUTPUT OPERATION

Although the AD7393 has been designed for single-supply op-

eration, the output can be easily configured for bipolar opera-

tion. A typical circuit is shown in Figure 30. This circuit uses a

clean regulated +5 V supply for power, which also provides the

circuit’s reference voltage. Since the AD7393 output span swings

from ground to very near +5 V, it is necessary to choose an exter-

nal amplifier with a common-mode input voltage range that

extends to its positive supply rail. The micropower consump-

tion OP196 has been designed just for this purpose and results

in only 50 microamps of maximum current consumption. Con-

nection of the equal valued 470 k

Ω resistors results in a differen-

tial amplifier mode of operation with a voltage gain of two,

which produces a circuit output span of ten volts (that is, –5 V

is set at –5 V, 0 V and +5 V (minus 1 LSB). The output voltage

D

512

–1











 × 5

Equation 4

where D is the decimal code loaded in the AD7393 DAC regis-

ter. Note that the LSB step size is 10/1024 = 10 mV. This cir-

cuit has been optimized for micropower consumption including

the 470 k

Ω gain setting resistors, which should have low tem-

perature coefficients to maintain accuracy and matching (prefer-

ably the same resistor material, such as metal film). If better

stability is required, the power supply could be substituted with

a precision reference voltage such as the low drop out REF195,

which can easily supply the circuit’s 162

µA of current, and still

micropower REF195 is guaranteed to source 10 mA output

drive current, but only consumes 50

µA internally. If higher

resolution is required, the AD7392 can be used with the addi-

tion of two more bits of data inserted into the software coding,

which would result in a 2.5 mV LSB step size. Table III shows

Operation circuit application.

C

REF

GND

<100 A

<2 A

470k

+5V

OP196

470k

+5V

–5V

BIPOLAR

OUTPUT

SWING

–5V

AD7393

DIGITAL INTERFACE CIRCUITRY OMITTED FOR CLARITY

<50 A

Figure 30. Bipolar Output Operation

Table III. Bipolar Code Table

Hexadecimal

Decimal

Analog

Number

Number

Output

In DAC Register

in DAC Register

Voltage (V)

3FF

1023

4.9902

201

513

0.0097

200

512

0.0000

1FF

511

–0.0097

000

0

–5.0000