ADC3641 datasheet(27/77 Pages) TI

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8.3.3 Voltage Reference

The ADC364x provides three different options for supplying the voltage reference to the ADC. An external 1.6 V

reference can be directly connected to the VREF input; a voltage 1.2 V reference can be connected to the

REFBUF input using the internal gain buffer or the internal 1.2 V reference can be enabled to generate a 1.6 V

reference voltage. For best performance, the reference noise should be filtered by connecting a 10 μF and a 0.1

μF ceramic bypass capacitor to the VREF pin. The internal reference circuitry of the ADC364x is shown in Figure

8-14.

Note

The voltage reference mode can be selected using SPI writes or by using the REFBUF pin (default) as

a control pin (Section 8.5.1).

If the REFBUF pin is not used for configuration, the REFBUF pin should be connected to AVDD (even

though the REFBUF pin has a weak internal pullup to AVDD) and the voltage reference option has to

be selected using the SPI interface.

xINP

xINM

VREF

(1.6V)

REFBUF

(1.2V)

REFGND

VREF1.2

VCM

0.95V

x1.33

Figure 8-14. Different voltage reference options for ADC364x

8.3.3.1 Internal voltage reference

The 1.6 V reference for the ADC can be generated internal using the on-chip 1.2 V reference along with the

internal gain buffer. A 10 μF and a 0.1 μF ceramic bypass capacitor (C VREF) should connected between the

VREF and REFGND pins as close to the pins as possible.

xINP

xINM

VREF

(1.6V)

REFBUF

(1.2V)

REFGND

VREF1.2

VCM

0.95V

X1.33

CVREF

Figure 8-15. Internal reference

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ADC3643

SBAS886 – OCTOBER 2020

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