COMBOSMARTMETER datasheet(22/60 Pages) TI1

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To ADC Reference Inputs

VCAP1

VREFP

VREFN

Bandgap

2.4 V or 4 V

AVSS

(1)

110

130

Normalized Frequency (f /f

)

IN MOD

0.5

1.5

2.5

3.5

DR[2:0] = 110

DR[2:0] = 000

ADS131E04

ADS131E06

ADS131E08

SBAS561A – JUNE 2012 – REVISED APRIL 2013

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Figure 27. Transfer Function of On-Chip Decimation Filters

Until 4 fMOD for DR[2:0] = 000 and DR[2:0] = 110

REFERENCE

Figure 28 shows a simplified block diagram of the internal ADS131E0x 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 kΩ.

Figure 28. Internal Reference

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

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 2.4 V. In case of a 5-V analog supply, the internal reference can be set 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 driven externally. Figure 29

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

CONFIG3 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.

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