AD7392ARZ datasheet(15/20 Pages) AD

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AD7392/AD7393

Rev. C | Page 15 of 20

BIPOLAR OUTPUT OPERATION

Although the AD7393 is designed for single-supply operation,

the output can be easily configured for bipolar operation. A

typical circuit is shown in Figure 33. 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 external

amplifier with a common-mode input voltage range that extends

to its positive supply rail. The micropower consumption OP196

is designed just for this purpose and results in only 50 μA of

maximum current consumption. Connecting the two 470 kΩ

resistors results in a differential amplifier mode of operation

with a voltage gain of 2, which produces a circuit output span

of 10 V, that is, −5 V to +5 V. As the DAC is programmed from

zero-code 0x000 to midscale 0x200 to full scale 0x3FF, 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.

512

⎥⎦

⎤

⎢⎣

⎡

−

= D

(4)

where D is the decimal code loaded in the AD7393 DAC

Note that the LSB step size is 10/1024 = 10 mV. This circuit

is optimized for micropower consumption including the 470 kΩ

gain setting resistors, which should have low temperature

coefficients to maintain accuracy and matching (preferably the

same resistor material, such as metal film).

If better stability is required, the power supply may be substi-

tuted with a precision reference voltage such as the low dropout

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 consumes only 50 μA internally.

If higher resolution is required, the AD7392 can be used with

two additional bits of data inserted into the software coding,

which results in a 2.5 mV LSB step size. Table 8 shows examples

of nominal output voltages (VO) provided by the bipolar

operation circuit application.

VREF

GND

+5V

OP196

+5V

–5V

BIPOLAR

OUTPUT

SWING

–5V

AD7393

NOTES

1. DIGITAL INTERFACE CIRCUITRY OMITTED FOR CLARITY

<50µA

<100µA

ISY <162µA

<2µA

470kΩ

VOUT

VDD

Figure 33. Bipolar Output Operation

Table 8. Bipolar Code Table

DAC Register No.

Hexadecimal

Decimal

Analog Output Voltage (V)

0x3FF

1023

+4.9902

0x201

513

+0.0097

0x200

512

0.0000

0x1FF

511

−0.0097

0x000

−5.0000

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