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AD7393
(Rev.:RevA)

+3 V, Parallel Input Micropower 10- and 12-Bit DACs

Analog Devices 

AD7392/AD7393

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

operation is shown in Table II.

+2.7V TO +5.5V

R

0.01␮F

EXT

REF

1

VDD

AD7392

20

REF

19

VOUT

DIGITAL INTERFACE

CIRCUITRY OMITTED

FOR CLARITY

AGND/DGND

17, 18

0.1␮F

RL

Ն5k⍀

10␮F

CL

Ն100pF

Figure 29. AD7392 Unipolar Output Operation

Table II. Unipolar Code Table

Hexadecimal

Number

in DAC Register

FFF

801

800

7FF

000

Decimal

Number

in DAC Register

4095

2049

2048

2047

0

Output

Voltage (V)

VREF = 2.5 V

2.4994

1.2506

1.2500

1.2494

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 kΩ 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

to +5 V). As the DAC is programmed from zero-code 000H to

midscale 200H to full scale 3FFH, the circuit output voltage VO

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

VO is coded in offset binary according to Equation 4.

VO

=

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 kΩ 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

provide additional power for the load connected to VO. The

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

examples of nominal output voltages VO provided by the Bipolar

Operation circuit application.

ISY < 162␮A

+5V

470k⍀

470k⍀

C

<2␮A

<100␮A

<50␮A

+5V

REF

VDD

AD7393 VOUT

GND

OP196

–5V

BIPOLAR

VO OUTPUT

SWING

–5V

DIGITAL INTERFACE CIRCUITRY OMITTED FOR CLARITY

Figure 30. Bipolar Output Operation

Table III. Bipolar Code Table

Hexadecimal

Number

In DAC Register

3FF

201

200

1FF

000

Decimal

Number

in DAC Register

1023

513

512

511

0

Analog

Output

Voltage (V)

4.9902

0.0097

0.0000

–0.0097

–5.0000

–10–

REV. A

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