ADC3561 datasheet(34/85 Pages) TI

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8.3.3 Voltage Reference

The ADC356x provides three different options for supplying the voltage reference to the ADC. An external 1.6V

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

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

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

uF ceramic bypass capacitor to the VREF pin. The internal reference circuitry of the ADC356x is shown in Figure

8-17.

Note

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

as a control pin (Configuration using PINs only). 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.

AINP

AINM

VREF

(1.6V)

REFBUF

(1.2V)

REFGND

VREF1.2

VCM

0.95V

x1.33

Figure 8-17. Different voltage reference options for ADC356x

8.3.3.1 Internal voltage reference

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

internal gain buffer. A 10 uF and a 0.1 uF ceramic bypass capacitor (CVREF) should be connected between the

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

xINP

xINM

VREF

(1.6V)

REFBUF

(1.6V)

REFGND

VREF1.2

VCM

0.95V

x1.33

CVREF

Figure 8-18. Internal reference

ADC3561, ADC3562, ADC3563

SBAS990B – FEBRUARY 2021 – REVISED OCTOBER 2022

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