SBOA551 June   2022 INA240

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2One, Versus Two Reference Pins
  5. 3Bidirectional Current Sense Amplifier Topologies
    1. 3.1 Single-Stage Difference Amplifier
    2. 3.2 Difference Amplifier Input Followed by Noninverting Output Buffer
    3. 3.3 Voltage Feedback Multi-Stage Difference Amplifier
    4. 3.4 Single-Stage Current Feedback
    5. 3.5 Current Feedback Multi-Stage Difference Amplifier
    6. 3.6 Isolated Bidirectional Current Sensors
  6. 4Options for Driving Reference Pins and Input Referred Reference Error
  7. 5Resistor Divider as Reference
    1. 5.1 Resistor Divider and Equivalent Circuit
    2. 5.2 Reference Source Impedance Error in Difference Amplifier
    3. 5.3 Reference Source Impedance Error in Voltage Feedback Multi-Stage CSA
    4. 5.4 Reference Source Impedance Error in Current Feedback Multi-Stage CSA
    5. 5.5 Reference Source Impedance Error in Difference Amplifier with Output Buffer
  8. 6Examples
    1. 6.1 Calculating Reference Source Impedance Error in Difference Amplifier
    2. 6.2 Calculating Reference Source Impedance Error in Voltage Feedback Multi-Stage CSA
    3. 6.3 Calculating Reference Source Impedance Error in Current Feedback Multi-Stage CSA
  9. 7Summary

6 Examples

This section provides several example calculations using error equations found in previous sections. Bench verification was performed to corroborate the validity of this data. Calculations are based on typical device information, including resistor values, gain of each stage, and common-mode input voltage if the example is multi-stage.

Resistor value is influenced by process variation and vary from lot to lot. Within the same lot, different units will have different resistor values. With multi-stage, the output stage common mode is determined by CMFB circuitry if the front end is fully differential, which is true for the vast majority of CSA. Gain of each stage is not fixed, it can vary within a small range for production trim.

Due to these variations, the calculations should only be treated as guidelines in visualizing the impact of the source impedance on accuracy for typically manufactured devices. Such calculations should not be used to compensate for system error.