ADS8699IPWR datasheet(30/74 Pages) TI2

30 / 74 page

7.3.7.2 External Reference

For applications that require a better reference voltage or a common reference voltage for multiple devices, the

device provides a provision to use an external reference source along with an internal buffer to drive the ADC

reference pin. In order to select the external reference mode, the INTREF_DIS bit of the RANGE_SEL_REG

REFIO pin, which functions as an input. Any low-power, low-drift, or small-size external reference can be used in

this mode because the internal buffer is optimally designed to handle the dynamic loading on the REFCAP pin

that is internally connected to the ADC reference input. The output of the external reference must be

appropriately filtered to minimize the resulting effect of the reference noise on system performance. A typical

connection diagram for this mode is shown in Figure 7-12.

ADC

4.096 VREF

REFCAP

REFIO

AGND

10 PF

REFGND

CREF

AVDD

REF5040

(See the device datasheet for

a detailed pin configuration.)

AVDD

OUT

1 PF

RANGE_SEL_REG[6] = 1

(INTREF_DIS)

Figure 7-12. Device Connections for Using an External 4.096-V Reference

The output of the internal reference buffer appears at the REFCAP pin. A minimum capacitance of 10 µF must

be placed between the REFCAP and REFGND pins. Place another capacitor of 1 µF as close to the REFCAP

pin as possible for decoupling high-frequency signals. Do not use the internal buffer to drive external ac or dc

loads because of the limited current output capability of this buffer.

ADS8691, ADS8695, ADS8699

SBAS777B – DECEMBER 2016 – REVISED MARCH 2021

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ADS8699IPWR Datasheet(PDF) 30 Page - Texas Instruments