SBOA536 December   2021 INA240

 

  1.   Trademarks
  2. 1Introduction
  3. 2Grounding in DC Circuits
  4. 3Grounding in Isolated Current Sensing Applications
  5. 4Working Principle of Non-isolated Current Sense Amplifiers
    1. 4.1 Single or Multi-stage Difference Amplifier
    2. 4.2 Current Feedback
    3. 4.3 Switched Capacitor
    4. 4.4 Input Stage and Input Bias Current
  6. 5Grounding in Non-isolated Current-Sensing Applications
  7. 6Level Shifting for High-Voltage Current-Sensing Applications
  8. 7Grounding in Motor Current-Sensing Applications
    1. 7.1 Common-Mode Voltage of Motor Current Sense Amplifiers
    2. 7.2 Directionality of Motor Current-Sense Amplifiers
    3. 7.3 PCB Design for High-Performance Motor Drive
  9. 8Summary
  10. 9References

4 Working Principle of Non-isolated Current Sense Amplifiers

Shunt-based Current Sense Amplifiers (CSA), also known as current shunt monitors, measure current by amplifying the voltage drop across the shunt resistor while rejecting the influence from common-mode input voltage. Unless specifically noted, the term CSA represents non-isolated analog output current-sense amplifiers throughout this article.

Based on the location of the shunt resistor, current-sensing topologies are classified into three categories – high side, low side, and inline. While low side current sensing topology has the advantage of avoiding large common-mode voltage, it does come with drawbacks including ground disturbance. For high side, the CSA must solve the challenge of tolerating common-mode input voltage which is typically much higher than the power-supply voltage itself. Rather than working with constant common-mode input voltage, inline current sensing experiences PWM-type common-mode input which poses a unique set of challenges.

A general-purpose high-performance CSA that is suitable for high-side configuration must be capable of the following specifications: wide common-mode input range, high CMRR, low VOS, high gain, and high bandwidth. There are numerous other specifications, which together with those listed can be tailored to target a specific segment of applications. It is rare, if possible at all, to create a CSA that is suitable for all applications. One of the first challenges in designing with a general purpose CSA is to choose one that strips the high common-mode voltage while amplifying the differential input with sufficiently large gain.

Although the selection of analog output CSA is quite large, most are classified into three categories based on topology.