AD7606BSTZ datasheet(24/36 Pages) AD

24 / 36 page

AD7606/AD7606-6/AD7606-4

Data Sheet

Rev. D | Page 24 of 36

INTERNAL/EXTERNAL REFERENCE

The AD7606/AD7606-6/AD7606-4 contain an on-chip 2.5 V

band gap reference. The REFIN/REFOUT pin allows access to

the 2.5 V reference that generates the on-chip 4.5 V reference

internally, or it allows an external reference of 2.5 V to be applied

to the AD7606/AD7606-6/AD7606-4. An externally applied

reference of 2.5 V is also gained up to 4.5 V, using the internal

buffer. This 4.5 V buffered reference is the reference used by the

SAR ADC.

The REF SELECT pin is a logic input pin that allows the user to

select between the internal reference and an external reference.

If this pin is set to logic high, the internal reference is selected

and enabled. If this pin is set to logic low, the internal reference

is disabled and an external reference voltage must be applied

to the REFIN/REFOUT pin. The internal reference buffer is

always enabled. After a reset, the AD7606/AD7606-6/AD7606-4

operate in the reference mode selected by the REF SELECT pin.

Decoupling is required on the REFIN/REFOUT pin for both

the internal and external reference options. A 10 µF ceramic

capacitor is required on the REFIN/REFOUT pin.

The AD7606/AD7606-6/AD7606-4 contain a reference buffer

configured to gain the REF voltage up to ~4.5 V, as shown in

Figure 40. The REFCAPA and REFCAPB pins must be shorted

together externally, and a ceramic capacitor of 10 μF applied to

REFGND, to ensure that the reference buffer is in closed-loop

operation. The reference voltage available at the REFIN/REFOUT

pin is 2.5 V.

When the AD7606/AD7606-6/AD7606-4 are configured in

external reference mode, the REFIN/REFOUT pin is a high

input impedance pin. For applications using multiple AD7606

devices, the following configurations are recommended,

depending on the application requirements.

External Reference Mode

One ADR421 external reference can be used to drive the

REFIN/REFOUT pins of all AD7606 devices (see Figure 41).

In this configuration, each REFIN/REFOUT pin of the

AD7606/AD7606-6/AD7606-4 should be decoupled with at

least a 100 nF decoupling capacitor.

Internal Reference Mode

One AD7606/AD7606-6/AD7606-4 device, configured to operate

in the internal reference mode, can be used to drive the remaining

AD7606/AD7606-6/AD7606-4 devices, which are configured to

operate in external reference mode (see Figure 42). The REFIN/

REFOUT pin of the AD7606/AD7606-6/AD7606-4, configured

in internal reference mode, should be decoupled using a 10 µF

ceramic decoupling capacitor. The other AD7606/AD7606-6/

AD7606-4 devices, configured in external reference mode,

should use at least a 100 nF decoupling capacitor on their

REFIN/REFOUT pins.

BUF

SAR

2.5V

REF

REFCAPA

REFIN/REFOUT

REFCAPB

10µF

Figure 40. Reference Circuitry

AD7606

REF SELECT

REFIN/REFOUT

AD7606

REF SELECT

REFIN/REFOUT

100nF

0.1µF

100nF

AD7606

REF SELECT

REFIN/REFOUT

100nF

ADR421

Figure 41. Single External Reference Driving Multiple AD7606/AD7606-6/

AD7606-4 REFIN Pins

AD7606

REF SELECT

REFIN/REFOUT

10µF

AD7606

REF SELECT

REFIN/REFOUT

100nF

AD7606

REF SELECT

REFIN/REFOUT

100nF

VDRIVE

Figure 42. Internal Reference Driving Multiple AD7606/AD7606-6/AD7606-4

REFIN Pins

AD7606BSTZ Datasheet(PDF) 24 Page - Analog Devices

AD7606BSTZ Datasheet(HTML) 24 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

Datasheet Download

Link URL