ADS1294CZXGR datasheet(33/114 Pages) TI2

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100

100 k

OPA350

22 nF

0.1 F

+5 V

0.1 F

10 F

100 F

10 F

OUT

VIN

5 V

TRIM

1 F

REF5025

To VREFP

22 F

ToADCReferenceInputs

VCAP1

10 F

VREFP

VREFN

Bandgap

2.4Vor4V

AVSS

(1)

ADS1294, ADS1294R, ADS1296, ADS1296R, ADS1298, ADS1298R

www.ti.com

SBAS459K – JANUARY 2010 – REVISED AUGUST 2015

9.3.1.6 Reference

Figure 31 shows a simplified block diagram of the ADS129x internal reference. The reference voltage is

generated with respect to AVSS. When using the internal voltage reference, connect VREFN to AVSS.

(1)

For VREF = 2.4 V: R1 = 12.5 kΩ, R2 = 25 kΩ, and R3 = 25 kΩ. For VREF = 4 V: R1 = 10.5 kΩ, R2 = 15 kΩ, and R3 =

35 k

Ω.

Figure 31. Internal Reference

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

systems, choose capacitor values with a bandwidth that is limited to less than 10Hz, so that the reference noise

does not dominate the system noise. When using a 3-V analog supply, set the internal reference to 2.4 V. For a

5-V analog supply, set the internal reference to 4 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

CONFIG3 register. By default, the device wakes up in external reference mode.

Figure 32. External Reference Driver

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ADS1294CZXGR Datasheet(PDF) 33 Page - Texas Instruments

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