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REV. A–6–

AD7866

PIN CONFIGURATION

TOP VIEW

(Not to Scale)

AD7866

REF SELECT

CAP

AGND

CAP

REF

SCLK

DRIVE

OUT

DGND

RANGE

PIN FUNCTION DESCRIPTIONS

Pin No. Mnemonic Function

1 REF SELECT Internal/External Reference Selection. Logic input. If this pin is tied to GND, the on-chip 2.5 V reference

is used as the reference source for both ADC A and ADC B. In addition, pins V

REF

, D

CAP

A, and D

CAP

must be tied to decoupling capacitors. If the REF SELECT pin is tied to a logic high, an external refer-

ence can be supplied to the AD7866 through the V

REF

pin, in which case decoupling capacitors are

required on D

CAP

A and D

CAP

B. However, if the V

REF

pin is tied to AGND while REF SELECT is tied to

a logic low, an individual external reference can be applied to both ADC A and ADC B through pins

CAP

A and D

CAP

B, respectively. See the Reference Configuration Options section.

2, 9 D

CAP

B, D

CAP

A Decoupling capacitors are connected to these pins to decouple the reference buffer for each respective

ADC. The on-chip reference can be taken from these pins and applied externally to the rest of a system.

Depending on the polarity of the REF SELECT pin and the configuration of the V

REF

pin, these

pins can also be used to input a separate external reference to each ADC. The range of the external

reference is dependent on the analog input range selected. See the Reference Configuration

Options section.

3, 8 AGND Analog Ground. Ground reference point for all analog circuitry on the AD7866. All analog input signals

and any external reference signal should be referred to this AGND voltage. Both of these pins should

connect to the AGND plane of a system. The AGND and DGND voltages ideally should be at the

same potential and must not be more than 0.3 V apart, even on a transient basis.

4, 5 V

Analog Inputs of ADC B. Single-ended analog input channels. The input range on each channel is 0 V

to V

REF

or a 2  V

REF

range depending on the polarity of the RANGE pin upon the falling edge of CS.

6, 7 V

Analog Inputs of ADC A. Single-ended analog input channels. The input range on each channel is 0 V

to V

REF

or a 2  V

REF

range depending on the polarity of the RANGE pin upon the falling edge of CS.

10 V

REF

Reference Decoupling and External Reference Selection. This pin is connected to the internal reference

and requires a decoupling capacitor. The nominal reference voltage is 2.5 V, which appears at the pin;

however, if the internal reference is to be used externally in a system, it must be taken from either the

CAP

A or D

CAP

B pins. This pin is also used in conjunction with the REF SELECT pin when

applying an external ref

erence to the AD7866. See the REF SELECT pin description.

1 2 3 4 5 6 7 8 9 10 11 ... 23 24

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