COMBOSMARTMETER datasheet(47/60 Pages) TI1

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(b) Voltage Sensing with Single-Ended Input

(a) Voltage Sensing with Differential Input

INP

INN

Device

EMI

Filter

OPAMPOUT

OPAMPN

OPAMPP

(AVDD + AVSS)

OPAMP_REF

INP

INN

Device

EMI

Filter

OPAMPOUT

OPAMPN

OPAMPP

(AVDD + AVSS)

OPAMP_REF

To PGA

ADS131E04

ADS131E06

ADS131E08

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SBAS561A – JUNE 2012 – REVISED APRIL 2013

VOLTAGE SENSING

Figure 45 shows a simplified diagram of commonly-used differential and single-ended methods of voltage

sensing. A resistor divider network is used to step down the line voltage within the acceptable ADS131E0x input

range and then directly connect to the inputs (INP and INN) through an antialiasing RC filter formed by resistor

R3 and capacitor C. The common-mode bias voltage (AVDD + AVSS) / 2, can be obtained from the ADS131E0x

by either configuring the internal op amp in a unity-gain configuration using the RF resistor and setting bit 3 of the

CONFIG3 register, or it can be generated externally by using a simple resistor divider network between the

positive and negative supplies.

In either of the below cases (Figure 45a for a differential input and Figure 45b for a single-ended input), the line

voltage is divided down by a factor of [R2 / (R1 + R2)]. Values of R1 and R2 must be carefully chosen so that the

voltage across the ADS131E0x inputs (INP and INN) does not exceed the FSDI range of ADS131E0x (see

Table 12) over the full operating dynamic range of the energy meter.

Figure 45. Simplified Voltage Sensing Connections

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