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

4 Applications for Resistance at Input Pins of Current Sense Amplifiers

Table 4-1 is a non-comprehensive list of applications and reasons why a system needs resistors at the input pins (IN+ and IN-) for a current sense amplifier.

Table 4-1 Applications for Using Current Sense Amplifier (CSA) with Input Resistors
Application Type Application Benefits
Input differential (VSHUNT) filtering with input CDIFF capacitor as shown in Figure 4-1
  1. Filters out current noise and/or transient spikes
  2. Allows for use of low-distortion NPO/C0G CDIFF capacitor, thus a more precise cutoff frequency (fC)
Input common-mode voltage (VCM) filtering (with input CCM capacitors). See Figure 4-2.
  1. Attenuates a periodic bus or fast VCM transient, which reduces device output error/disturbances.
  2. Using higher REXT (thus lower CCM) helps reduce capacitive load on the bus rail.
  3. Note: When using CCM on input pins, the advise is to also use a CDIFF>10*CCM to help reduce CCM settling imbalances.
  4. Note: This is not recommended for PWM applications requiring high BW and fast settling times. Using a CSA with enhanced PWM rejection circuitry (for example, INA241 or INA240) is the recommended amplifier for these applications.
Input current limiting for input VCM violation events: ESD fast-transient or DC electrical overstress (EOS). See Figure 4-3.
  1. Protects device from damage by limiting current of amplifier input ESD cell activation and/or input latch up pathway
  2. Limits current of external protection clamping diodes, which reduces required diode power dissipation.
  3. Transient Robustness for Current Shunt Monitor, reference design.

For Figure 4-1, the input filter cutoff frequency is fC,differential = 1 / (2 × PI × 2 × RFILTER × CDIFF).

Current Sense Amplifier with Input Differential Filter Figure 4-1 Current Sense Amplifier with Input Differential Filter

For Figure 4-2, the input filter cutoff frequency is fC,differential = 1 / (2 × PI × 2 × RFILTER × (CDIFF + CCM / 2)).

Current Sense Amplifier With Input Common-Mode FilterFigure 4-2 Current Sense Amplifier With Input Common-Mode Filter
Current Sense Amplifier With Input Protection Diode Clamps and ResistorsFigure 4-3 Current Sense Amplifier With Input Protection Diode Clamps and Resistors