AD9260ASZ datasheet(30/45 Pages) AD

30 / 45 page

AD9260

Rev. C | Page 29 of 44

The actual reference voltages used by the internal circuitry of

the AD9260 appear on the CAPT and CAPB pins. If VREF is

configured for 2.5 V, thus providing a 4 V full-scale input span,

the voltages appear at CAPT and CAPB are 3.0 V and 1.0 V

respectively. For proper operation when using the internal or an

external reference, it is necessary to add a capacitor network to

decouple the CAPT and CAPB pins. Figure 67 shows the

recommended decoupling network. This capacitive network

performs the following three functions: (1) along with the

reference amplifier, A2, it provides a low source impedance over

a large frequency range to drive the A/D internal circuitry; (2) it

provides the necessary compensation for A2; and (3) it

bandlimits the noise contribution from the reference. The turn-

on time of the reference voltage appearing between CAPT and

CAPB is approximately 15 ms and should be evaluated in any

power-down mode of operation.

CAPT

CAPB

AD9260

µF

0.1

µF

0.1

µF

0.1

µF

0.1

µF

VREF

SENSE

REFCOM

Figure 67. Recommended Reference Decoupling Network

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