AD7352

Data Sheet

Rev. B | Page 14 of 20

+2.048V

+1.024V

GND

–2.048V

–5V

AD8138

OP177

2.048V

1.024V

0V

2.048V

1.024V

0V

AD7352

10kΩ

10kΩ

10µF

10µF

*MOUNT AS CLOSE TO THE AD7352 AS POSSIBLE.

+5V

+2.5V

+5V

+2.25V TO +3.6V

–5V

+2.048V

AGND DGND

Figure 20. Using the AD8138 as a Single-Ended-to-Differential Amplifier

If the analog inputs source being used has zero impedance, all

as each other. If the source has a 50 Ω impedance and a 50 Ω

balance this parallel impedance on the input and thus ensure

that both the positive and negative analog inputs have the

same gain. The outputs of the amplifier are perfectly matched,

balanced differential outputs of identical amplitude, and are

exactly 180° out of phase.

Op Amp Pair

An op amp pair can be used to directly couple a differential

signal to one of the analog input pairs of the AD7352. The

circuit configurations in Figure 21 and Figure 22 show how an

op amp pair can be used to convert a single-ended signal into

a differential signal for both a bipolar and unipolar input signal,

respectively.

The voltage applied to Point A sets up the common-mode

voltage. In both diagrams, it is connected in some way to the

reference. The AD8022 is a suitable dual op amp that could be

used in this configuration to provide differential drive to the

AD7352.

GND

27Ω

27Ω

V+

V–

V+

V–

1.024V

2.048V

0V

1.024V

2.048V

0V

AD7352*

220Ω

10µF

*ADDITIONAL PINS OMITTED FOR CLARITY.

220Ω

220Ω

10kΩ

10kΩ

A

220Ω

2

Figure 21. Dual Op Amp Circuit to Convert a Single-Ended Unipolar Signal

into a Differential Signal

GND

27Ω

27Ω

V+

V–

V+

V–

1.024V

2.048V

0V

1.024V

2.048V

0V

AD7352*

220Ω

10µF

*ADDITIONAL PINS OMITTED FOR CLARITY.

220Ω

220Ω

20kΩ

A

440Ω

10kΩ

220Ω

Figure 22. Dual Op Amp Circuit to Convert a Single-Ended Bipolar Signal into

a Differential Unipolar Signal

VOLTAGE REFERENCE

The AD7352 allows the choice of a very low temperature drift

internal voltage reference or an external reference. The internal

2.048 V reference of the AD7352 provides excellent perfor-

mance and can be used in almost all applications. When the

internal reference is used, the reference voltage is present on

REFGND with 10 μF capacitors. The internal reference voltage

can be used elsewhere in the system, provided it is buffered

externally.

external voltage reference if desired. The applied reference

choice would be to use an external 2.5 V reference such as the

ADR441 or ADR431.

ADC TRANSFER FUNCTION

The output coding for the AD7352 is straight binary. The designed

code transitions occur at successive LSB values (1 LSB, 2 LSBs,

characteristic is shown in Figure 23.

000 ... 000

000 ... 001

000 ... 010

111 ... 101

111 ... 110

111 ... 111

ANALOG INPUT

Figure 23. AD7352 Ideal Transfer Characteristic