Zero drift PGA based Analog Front End Design for Circuit Breakers (ACB/MCCB-ETU)


Design files


This reference design is intended for use in molded case circuit breakers (MCCB) electronic trip units.  The programmable gain amplifier based design acts as the current monitoring for over-current earth fault relays. Utilizing a zero drift programmable amplifier, this design provides a ±10 % pick-up (A) accuracy  and time delay (s) accuracy of 0 to -20%. Additionally, this solution was designed to handle harsh environment conditions by including features such as ambient insensitivity from -10 to 70 ⁰C and high electromagnetic immunity. Finally the analog front end of this design interfaces seemlessly with the TI MSP430 MCU for quicker evaluation and faster time-to-market.

  • Architecture enables the customer to easily create multiple circuit breaker models with different current ranges
  • Using programmable gain control, fault current sensing range can be increased to > 10 times Ir and < 0.2 times Ir
  • Lower total manufacturing cost with reduced component count and less calibration time vs. discrete opamp based electromechanical solution
  • Robust design with ambient insensitivity from -10 to +70°C and better trip time repeatability vs. discrete opamp based electromechanical solution
  • Wide input DC-DC converter with under voltage and overcurrent protection
  • Self-power (CT powered) supply with reduced CT loading and lower power loss
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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

Download ready-to-use system files to speed your design process.

TIDU230A.PDF (1868 K)

Reference design overview and verified performance test data

TIDR461.PDF (421 K)

Detailed schematic diagram for design layout and components

TIDR462.PDF (207 K)

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

TIDC322.ZIP (2542 K)

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

TIDU260.PDF (2355 K)

PCB layer plot file used for generating PCB design layout


Includes TI products in the design and potential alternatives.

Analog temperature sensors

LM62±2°C analog output temperature sensor, with 15.6mV/°C gain

Data sheet: PDF
Isolated DC/DC converters & modules

LM50177.5-100V Wide Vin, 600mA Constant On-Time Synchronous Buck Regulator

Data sheet: PDF | HTML
Isolated DC/DC converters & modules

TPS550102.95V To 6V Input, 2W, Isolated DC/DC Converter with Integrated FETS

Data sheet: PDF | HTML
N-channel MOSFETs

CSD18537NKCS60-V, N channel NexFET™ power MOSFET, single TO-220, 14 mOhm

Data sheet: PDF | HTML
Programmable & variable gain amplifiers (PGAs & VGAs)

PGA117Zero-drift, 100-µV offset, 12-nV/√Hz noise, RRO (scope gain) programmable gain amp with 10-ch mux

Data sheet: PDF | HTML
Shunt voltage references

LM4041BAdjustable, precision micropower shunt voltage reference with 0.2% accuracy

Data sheet: PDF

Technical documentation

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* Design guide Zero-Drift Analog Front End PGA and Peripherals for MCCB Design Guide (Rev. A) Apr. 17, 2014

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