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

3.2 Difference Amplifier Input Followed by Noninverting Output Buffer

As Figure 3-2 shows, by attaching a noninverting output stage to the single-stage difference amplifier, a two-stage CSA with potentially very high gain is developed. Aside from flexibility in gain configuration, the intermediate output can be brought out as an optional output pin. The overall performance is dominated by the first stage, therefore much of the same performance limitations remain as with single-stage difference amplifier. Compared with other multistage alternatives discussed in the next sections, the added output stage does not significantly improve critical electrical performance.

Figure 3-2 Difference Amplifier Followed by Noninverting Output Buffer

The device gain is the product of the gains of all stages, and the transfer function is written as:

Equation 2. Vout_ideal=RfRi1+Rf_2Ri_2Vdiff+Vref_x