Datasheet

Internal

Reference

AVDD AGND

REF

REFGND

10 F

ADC

Configuration

Internal

Reference

AVDD AGND

REF

REFGND

REF30/50xx

AGND

Plane

AVDD

Plane

1 F

ADC

Configiguration

ADS8634

ADS8638

SBAS541A –MAY 2011– REVISED AUGUST 2011

www.ti.com

The ADS8634/8 sample the voltage difference (V

AINx

– V

AINGND

) between the selected analog input channel and

the AINGND pin. The ADS8634/8 allow a ±0.2V range on AINGND. This feature is useful in modular systems

where the sensor/signal conditioning block is removed from the ADC and when there could be a difference in the

ground potential of the sensor/signal condioner from the ADC ground. In such cases, it is recommended to run

separate wires from the AINGND terminal of the device to the sensor/signal conditioner ground.

REFERENCE

The ADS8634/8 measure the analog input signals relative to the voltage reference using either an internal

precision 2.5V voltage reference (Figure 73) or an external voltage reference (Figure 74). Binary-weighted

capacitors are switched onto the reference terminal during conversion. The switching frequency is the same as

the SCLK frequency. Whether it is an internal or external reference, be sure to decouple the REF terminal to

REFGND with a 10µF capacitor. Place the capacitor close to the REFP and REFGND pins.

Figure 73. Operation Using The Internal Reference

(Refer to Table 11 for more details on the configuration register settings)

Figure 74. Operation Using an External Reference

(Refer to Table 11 for more details on the configiguration register settings)

Product Folder Link(s): ADS8634 ADS8638