AD8270ACPZ-R7 datasheet(18/20 Pages) AD

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AD8270

Data Sheet

Rev. A | Page 18 of 20

DRIVING AN ADC

The high slew rate and drive capability of the AD8270, combined

with its dc accuracy, make it a good analog-to-digital converter

(ADC) driver. The AD8270 can drive both single-ended and

differential input ADCs. Many converters require the output to

be buffered with a small value resistor combined with a high

quality ceramic capacitor. See the converter data sheet for more

details. Figure 51 shows the AD8270 in differential configuration,

driving the AD7688 ADC. The AD8270 divides down the 5 V

reference voltage from the ADR435, so that the common-mode

output voltage is 2.5 V, which is precisely where the AD7688

needs it.

DRIVING CABLING

All cables have a certain capacitance per unit length, which varies

widely with cable type. The capacitive load from the cable may

cause peaking or instability in output response, especially when the

AD8270 is operating in a gain of 0.5.

To reduce the peaking, use a resistor between the AD8270 and the

cable. Because cable capacitance and desired output response vary

widely, this resistor is best determined empirically. A good starting

point is 20 Ω.

AD8270

(DIFF OUT)

AD8270

(SINGLE OUT)

Figure 50. Driving Cabling

10kΩ

20kΩ

10kΩ

0.1µF

5V_REF

AD8270

–IN

+IN

–IN

+IN

+12V –12V

33Ω

2.7nF

COG

33Ω

2.7nF

COG

4 –IN

+IN

REF

AD7688

0.1µF

ADR435

GND

VIN

VOUT

+12V

10µF

5V_REF

NOTE:

POWER SUPPLY DECOUPLING

NOT SHOWN.

Figure 51. Driving an ADC

AD8270ACPZ-R7 Datasheet(PDF) 18 Page - Analog Devices

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