Extended Current and Voltage Measurement Using Shunts for Protection Relays Reference Design


Design files


This reference design demonstrates a unique approach for extending current measurement range using a single shunt and voltage measurement AMC1304Mx5 isolated delta-sigma (ΔΣ) modulator. With careful selection of a low-value shunt resistor that minimizes power dissipation, a front-end amplifier with low noise and by introducing two gain paths, both upper and lower current limit is extended.  Accuracy of < ±0.5 % for both current and voltage measurement is achieved by interfacing the modulator output to AM437x host processor which performs the Sinc3 filtering.

  • Single-phase voltage and current measurement (shunt based) using isolated delta-sigma modulator (AMC1304Mx5)
  • Measurement accuracy:
    • AC current: < ± 0.5% from 0.1 A to 40 A (or 60 A) for In = 1 A
    • AC voltage: < ± 0.5% from 10 V to 300 V
  • AFE interfaced to host MCU (AM437x Sitara™ ARM® Cortex®-A9 processor) which performs Sinc3 digital filtering using PRU-ICSS
  • Onboard isolated ± 2.5-V and +5.0-V Power supply for AMC1304Mx5 and OPA188 using transformer driver and LDOs
  • Designed to work from 0.1 A to 60 A (In = 1 A) and can be extended for wider range (In = 5 A) by changing shunt and gain values.
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A fully assembled board has been developed for testing and performance validation only, and is not available for sale.

Design files & products

Design files

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TIDRJM5.PDF (1107 K)

Detailed schematic diagram for design layout and components


Complete listing of design components, reference designators, and manufacturers/part numbers


Detailed overview of design layout for component placement


Detailed overview of design layout for component placement

TIDRJN0.ZIP (2563 K)

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Design file that contains information on physical board layer of design PCB

TIDRJM9.PDF (3666 K)

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Includes TI products in the design and potential alternatives.

Isolated ADCs

AMC1304M05±50-mV input, precision current sensing reinforced isolated modulator with LDO

Data sheet: PDF | HTML
Isolated ADCs

AMC1304M25±250-mV input, precision current sensing reinforced isolated modulator with LDO

Data sheet: PDF | HTML
Clock buffers

CDCLVC1104Low jitter, 1:4 LVCMOS fan-out clock buffer

Data sheet: PDF | HTML
Linear & low-dropout (LDO) regulators

TLV704150-mA 24-V ultra-low-IQ low-dropout (LDO) voltage regulator

Data sheet: PDF | HTML
Linear & low-dropout (LDO) regulators

TPS709150-mA, 30-V, ultra-low-IQ, low-dropout voltage regulator with reverse current protection and enable

Data sheet: PDF | HTML
Linear & low-dropout (LDO) regulators

TPS7A3001-EPEnhanced product, negative VIN, 200-mA, ultra-low noise, high PSRR, LDO regular

Data sheet: PDF
Precision op amps (Vos<1mV)

OPA188Precision, Low-Noise, Rail-to-Rail Output, 36V Zero-Drift Operational Amplifier

Data sheet: PDF | HTML
Transformer drivers

SN6501Low-noise, 350-mA, 410-kHz transformer driver for isolated power supplies

Data sheet: PDF | HTML

Technical documentation

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Type Title Date
* User guide Wide Input Current Using Shunts and Voltage Measurement for Protection Relays Dec. 04, 2015

Related design resources

Reference designs

TIDA-00080 Isolated delta-sigma modulator based AC/DC voltage and current measurement module reference design TIDA-00555 Isolated Current & Voltage Measurement Using Fully Differential Isolation Amplifier Reference Design

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