TIDUEH2C April   2021  – September 2022

 

  1.   Description
  2.   Resources
  3.   Features
  4.   Applications
  5.   5
  6. 1System Description
    1. 1.1 Key System Specifications
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
    3. 2.3 Highlighted Products
      1. 2.3.1 OPA365-Q1 (50 MHz)
      2. 2.3.2 OPA607-Q1 (50 MHz)
      3. 2.3.3 OPA836 (same as OPA2836-Q1) (205 MHz)
      4. 2.3.4 OPA863 (50 MHz)
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
    2. 3.2 Test Setup
      1.      19
    3. 3.3 Test Results
  9. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
    2. 4.2 Documentation Support
    3. 4.3 Support Resources
    4. 4.4 Trademarks
  10. 5About the Author
  11. 6Revision History

1 System Description

A low-side current shunt is a simple, low cost way to measure wideband current signals up to ± 100 A, with a greater degree of accuracy and dynamic range when compared with magnetic and in-phase current sensing.

In the current shunt circuit, the amplifier’s gain (AV/V) is required to minimize shunt power (Wshunt) and amplify the shunt's voltage signal up to the full ADC input range. A sufficient gain allows a minimized shunt resistance (Rshunt) and ensures that a maximized signal-to-noise ratio is being sent to the analog-to-digital converter (ADC). The amplifier's bandwidth is required to measure a short minimum pulse width so that a high pulse-width-modulation frequency (fPWM) can be used to control phase current. This design guide will compare three high gain-bandwidth product devices and review the necessary considerations for fast and accurate current sensing.

Magnetic solutions like Rogowski coils and current transformers are optimized to measure alternating currents within a frequency range, but their bandwidth and dynamic range are constrained by the derivative relationship between magnetic field strength and current frequency. DC currents cannot be measured and can saturate the core of a current transformer. Alternatively, in-phase shunt monitors require an amplifier with an input common-mode voltage range up to and above the maximum system voltage. The large input common-mode step that occurs during switching injects noise into the measurement. This method can add to the complexity and cost of the overall design. A low-side shunt can measure a wide range of current over a wide bandwidth and minimize design complexity and cost.