TIDUFG2 December   2025

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Terminology
    2. 1.2 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Sensor Selection
    3. 2.3 Highlighted Products
      1. 2.3.1 TLV387
      2. 2.3.2 TLV9054
      3. 2.3.3 MSPM0G5187-LP
      4. 2.3.4 LOG300
      5. 2.3.5 UCC28881
      6. 2.3.6 TPS709
  9. 3System Design Theory
    1. 3.1 Current Sensor
    2. 3.2 Hybrid Integrator
    3. 3.3 Band-Pass Filter
      1. 3.3.1 Log Amplifier
      2. 3.3.2 Current Low-Pass Filter
      3. 3.3.3 Non-isolated Voltage Sensing
      4. 3.3.4 Auto Labeling Circuit
        1. 3.3.4.1 Line Voltage Sensing
        2. 3.3.4.2 Arc Gap Voltage Sensing
        3. 3.3.4.3 Differential to Single-Ended Conversion
      5. 3.3.5 Power Supply
  10. 4Hardware, Software, Testing Requirements, and Test Results
    1. 4.1 Hardware Requirements
    2. 4.2 Software
    3. 4.3 Test Setup
      1. 4.3.1 Arc Testing Setup
    4. 4.4 Test Results
  11. 5Design and Documentation Support
    1. 5.1 Design Files
      1. 5.1.1 Schematics
      2. 5.1.2 BOM
    2. 5.2 Tools and Software
    3. 5.3 Documentation Support
    4. 5.4 Support Resources
    5. 5.5 Trademarks
  12. 6About the Author

3.2 Hybrid Integrator

TIDA-010971 Hybrid Integrator Schematic Figure 3-4 Hybrid Integrator Schematic

An integrator provides flat linear response across the full PCB Rogowski bandwidth and amplifies the signal at low frequencies. An integrator has infinite gain at DC. This causes errors to accumulate over time requiring integrator reset. This design avoids that problem by using feedback resistor R6 on the amplifier. R6 and R3 then set the DC gain.

Amplifier noise drives integrator amplifier selection. Rogowski sensitivity calculates at 4µV/A at 60Hz using equations in TIDA-01063. Noise around 8nV provides about 2% accuracy. The Rogowski acts as a high-pass filter. Higher frequencies have larger signals. 1mA at 60kHz with 4nV noise gives 2% accuracy. Similarly, 1µA at 60MHz provides 2% accuracy. TLV387 meets this low noise requirement.

The corner frequency of the integrator is selected above 60hz at 1kHz to attenuate the load signal and provide a sharper cutoff for the band-pass filter.

At 1kHz, the open loop gain reaches 75dB. The DC gain is set at 68.6dB (R6 and R3), or 2543v/v. This represents the upper limit of gain that the amplifier supports with some margin. The phase margin for this circuit simulates to 45.61°. At 2543v/v with 4µV/A sensitivity the integrator output voltage/A at 60Hz equals 10mV/A at 60Hz.

The active low-pass filter has bandwidth limitations. However, a passive RC filter extends the bandwidth. The passive filter must have a cutoff frequency at the crossover frequency of the designed active low-pass filter(2). With 68.6dB gain the crossover frequency occurs at 2MHz. R3 and C5 are chosen with a cutoff frequency at 2MHz extending the integrator bandwidth.

TIDA-010971 Integrator Without Low-Pass Filter Figure 3-5 Integrator Without Low-Pass Filter
TIDA-010971 Final Hybrid Integrator Magnitude and Phase After Low-Pass Filter is Added Figure 3-6 Final Hybrid Integrator Magnitude and Phase After Low-Pass Filter is Added

At this gain the input offset voltage also amplifies. At 0V to 3.3V range the maximum offset voltage with no margin for the signal equals 1.29mV. For TLV387 the maximum input offset voltage reaches 10µV. This leads to ±25mV DC offset that cancels with a high-pass filter in the band-pass stage. Considering the offset, the adjusted range over temp of the amplifier equals 3.3V – 0.25V = 3.05V. The maximum current that can be sensed without clipping with this hybrid integrator calculates as:

Equation 2. ( a d j u s t e d r a n g e ) / ( g a i n × s e n s i t i v i t y ) = 3.25 V / ( 2543 × 4 μ V / A ) = 320 A

For this design TLV387 is chosen for low noise and low input offset. These characteristics enable significant amplification of the small signal from the PCB Rogowski. A single amplifier makes the hybrid integrator topology work for high bandwidth applications. The passive RC low-pass filter extends the amplifier bandwidth. For designs not needing higher bandwidth, a two-stage integrator + amplifier works with OPAx323 or TLV905x. This negates the input offset voltage causing clipping, but limits the integrator bandwidth by the second stage amplifier.

Table 3-1 Amplifier Comparison
AMPLIFIER TLVx387 OPAx323 TLV905x
Number of channels 1, 2, 4 1, 2, 4 1, 2, 4
Noise 9nV/√Hz 5.5nV/√Hz 20nV/√Hz
Bandwidth 5.7MHz 20MHz 5.5MHz
Quiescent current 570μA 1.6mA 330μA

Maximum input offset voltage

(–40°C to 120°C)		 10μV 1.35mV 2mV
Input offset voltage typical 1μV 150μV 330μV