ADS1292 datasheet(25/69 Pages) TI

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1 F

To ADC Reference Inputs

VCAP1

10 F

VREFP

VREFN

Bandgap

2.42 V or

4.033 V

AVSS

(1)

0.1 F

100 W

100kW

100 W

OPA211

10pF

0.1 F

+5V

0.1 F

10 F

100 F

22 F

OUT

VIN

+5V

TRIM

22 F

REF5025

ToVREFPPin

ADS1291

ADS1292

ADS1292R

www.ti.com

SBAS502A – DECEMBER 2011 – REVISED MARCH 2012

REFERENCE

Figure 31 shows a simplified block diagram of the ADS1291, ADS1292, and ADS1292R internal reference. The

reference voltage is generated with respect to AVSS. The VREFN pin must always be connected to AVSS.

(1) For VREF = 2.42 V: R1 = 100 kΩ, R2 = 200 kΩ, and R3 = 200 kΩ. For VREF = 4.033 V: R1 = 84 kΩ, R2 = 120 kΩ, and R3 = 280 kΩ.

Figure 31. Internal Reference

The external band-limiting capacitors determine the amount of reference noise contribution. For high-end ECG

systems, the capacitor values should be chosen such that the bandwidth is limited to less than 10 Hz so that the

reference noise does not dominate the system noise. When using a 3-V analog supply, the internal reference

must be set to 2.42 V. In case of a 5-V analog supply, the internal reference can be set to 4.033 V by setting the

VREF_4V bit in the CONFIG2 register.

Alternatively, the internal reference buffer can be powered down and VREFP can be applied externally. Figure 32

shows a typical external reference drive circuitry. Power-down is controlled by the PD_REFBUF bit in the

CONFIG2 register. This power-down is also used to share internal references when two devices are cascaded.

By default the device wakes up in external reference mode.

Figure 32. External Reference Driver

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