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

6.3 Calculating Reference Source Impedance Error in Current Feedback Multi-Stage CSA

The INA241 and INA296 family of devices take advantage of the current feedback front end and isolates the rest of the circuits from the high input common-mode voltage. The following relevant design parameters are known (refer to Figure 5-5): Ri = 10 kΩ; RL = 106 kΩ; Rf = 500 kΩ; Vbias = –9 V which is achieved through negative charge pump for Vs = 5 V.

The output error terms are calculated for the following condition: Vs = 5 V; Vref_x = 2.5 V; Vdiff = 50 mV. The results are shown in Table 6-4.

Table 6-4 Reference Source Impedance Error for INA241A3
Rx (kΩ) C = Rx / (RL + Rf) m = C / (1 + C) Err_Vref (mV) Err_Vcm (mV) Err_Vdiff (mV) Err_Total (mV)
1 0.0017 0.0016 –4.12 –14.83 0.44 –18.51
5 0.0083 0.0079 –20.46 –73.65 2.17 –91.94
10 0.0165 0.0157 –40.58 –146.10 4.30 –182.39
20 0.0330 0.0310 –79.87 –287.54 8.47 –358.95
30 0.0495 0.0458 –117.92 –424.53 12.50 –529.95
40 0.0660 0.0602 –154.80 –557.28 16.41 –695.67
50 0.0825 0.0741 –190.55 –685.98 20.20 –856.33