AD7643 datasheet(16/24 Pages) AD

16 / 24 page

AD7625

Data Sheet

Rev. A | Page 16 of 24

DRIVING THE AD7625

Differential Analog Input Source

Figure 24 shows an ADA4899-1 driving each differential input

to the AD7625.

Single-Ended-to-Differential Driver

For applications using unipolar analog signals, a single-ended-

to-differential driver, as shown in Figure 23, allows for a differ-

ential input into the part. This configuration, when provided

with an input signal of 0 V to 4.096 V, produces a differential

±4.096 V with midscale at 2.048 V. The one-pole filter using

R = 33 Ω and C = 56 pF provides a corner frequency of 86 MHz.

The VCM output of the AD7625 can be buffered and then used

to provide the required 2.048 V common-mode voltage.

56pF

33Ω

50Ω

IN+

IN–

AD7625

VCM

V–

V+

AD8031, AD8032

ADA4899-1

56pF

100nF

590Ω

ANALOG INPUT

(UNIPOLAR 0V TO 4.096V)

Figure 23. Single-Ended-to-Differential Driver Circuit

56pF

33Ω

–VS

0V TO VREF

+VS

56pF

33Ω

–VS

VREF TO 0V

+VS

CREF

10µF2

REF1

REF

GND

IN+

IN–

AD7625

ADA4899-1

1SEE THE VOLTAGE REFERENCE OPTIONS SECTION. CONNECTION TO EXTERNAL REFERENCE SIGNALS

IS DEPENDENT ON THE EN1 AND EN0 SETTINGS.

2CREF IS USUALLY A 10µF CERAMIC CAPACITOR WITH LOW ESL AND ESR.

THE REF AND REFIN PINS ARE DECOUPLED REGARDLESS OF EN1 AND EN0 SETTINGS.

VCM

–VS

+VS

BUFFERED VCM PIN OUTPUT

GIVES THE REQUIRED 2.048V

COMMON-MODE SUPPLY FOR

ANALOG INPUTS.

VCM

2.048V

AD8031, AD8032

ADA4899-1

REFIN

REF1

CREF

10µF2

0.1µF

Figure 24. Driving the AD7625 from a Differential Analog Source

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