SLYA042 July   2024 FDC1004 , FDC1004-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1 Introduction
  5. 2 CSAs and Input Bias Stage
  6. 3 CSA and Gain Error Factor
  7. 4 Applications for Resistance at Input Pins of Current Sense Amplifiers
    1. 4.1 Input Resistance Design Considerations
  8. 5 Applications for Input Resistance at Reference Pins of Current Sense Amplifiers
    1. 5.1 Bidirectional CSA and Applications
    2. 5.2 Driving CSA Reference Pin With High-Resistance Source Voltage
    3. 5.3 Input Resistance at Reference Pin Design Considerations
  9. 6 Design Procedure and Error Calculation for External Input Resistance on CSA
    1. 6.1 Calculating eEXT for INA185A4 With 110Ω Input Resistors
  10. 7 Design Procedure for Input Resistance on Capacitively-Coupled Current Sense Amplifier
    1. 7.1 Bench Verification of Input eEXT for Capacitively-Coupled Current Sense Amplifiers
  11. 8 Design Procedure for Input Resistance at CSA Reference Pins
  12. 9 Input Resistance Error Test with INA185 Over Temperature
    1. 9.1 Schematic
    2. 9.2 Methods
    3. 9.3 Theoretical Model
    4. 9.4 Data for INA185A4 with 110Ω Input Resistors
      1. 9.4.1 Data Calculations
    5. 9.5 Analysis
  13. 10Input Resistance Error Test with INA191 Over Temperature
    1. 10.1 Schematic
    2. 10.2 Methods
    3. 10.3 Theoretical Model
    4. 10.4 Data for INA191A4 With 2.2kΩ Input Resistors
      1. 10.4.1 Data Analysis
    5. 10.5 Analysis
  14. 11Derivation of VOS, EXT for a Single Stage Current Sense Amplifier (CSA)
  15. 12Summary
  16. 13References

7 Design Procedure for Input Resistance on Capacitively-Coupled Current Sense Amplifier

When using REXT >100-Ω with the INA190 or similar CSA with capacitive-coupled input, the procedure for determining the error is outlined in the following.

  1. Based upon the maximum possible operating temperature, determine the input differential resistance (RDIFF) values at the nominal operating temperature (25°C) and maximum (TA, high) and minimum temperatures (TA, low).
    1. This data plot (for example, Figure 1-2) can be available in the data sheet.
  2. Calculate GEF for each temperature using the equation provided in data sheet as shown in Equation 18.
    1. Calculate EG, EXT at each temperature as 1-GEF
  3. Using values from step 2, calculate the drift in external loading gain error using Equation 19.
    1. Note EG, EXT can decrease significantly at increasing temperatures so try to choose two values that correspond linearly the best with the roll-off in gain.
  4. The new typical circuit gain at 25°C needs to be calculated using Equation 3.
Equation 18. GEFCapacitive-Coupled = RDIFFRDIFF + RSH + 2×REXT
Equation 19. EG Drift, EXTHigh-Nominal = EG EXT, TA, High - EG EXT, TA, NominalTA, High - TA, Nominal×106EG Drift, EXTLow-Nominal = EG EXT, TA, Low - EG EXT, TA, NominalTA, Low - TA, Nominal×106