COMBOSMARTMETER datasheet(46/60 Pages) TI1

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(a) Current Output CT with Differential Input

(b) Voltage Output CT with Single-Ended 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

SBAS561A – JUNE 2012 – REVISED APRIL 2013

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CURRENT SENSING

Figure 44 shows a simplified diagram of typical configurations used for current sensing with a Rogowski coil,

current transformer (CT), or an air coil that outputs a current or voltage. In the case of the current output

transformers, the burden resistors (R1) are used for current-to-voltage conversion. The output of the burden

resistors is connected to the ADS131E0x INP and INN inputs through an antialiasing RC filter for current

sensing. In the case of the voltage output transformers (such as certain types of Rogowski coils), the output

terminals of the transformers are directly connected to the ADS131E0x INP and INN inputs through an

antialiasing RC filter for current sensing. 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 with a simple resistor divider network

between the positive and negative supplies.

The value of resistor R1 for the current output transformer and turns ratio of the transformer should be selected

so as not to exceed the ADS131E0x full-scale differential input voltage (FSDI) range. Likewise, the output

voltage (V) for the voltage output transformer should be selected to not exceed the FSDI. In addition, the

selection of resistor (R) and turns ratio should not saturate the transformer over the full operating dynamic range

of the energy meter. Figure 44a shows differential input current sensing and Figure 44b shows single-ended

input sensing.

Figure 44. Simplified Current Sensing Connections

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Product Folder Links: ADS131E04 ADS131E06 ADS131E08

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