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

10.2 Methods

EVM shunt resistor pads were populated a 1Ω shunt resistor, which was measured with a 4-wire force and sense Ohm meter inside a temperature chamber at -40°C, 25°C, and 125°C. The input resistors chosen for the input pins (REXT1 at IN+ and REXT2 at IN-) were 2.2kΩ resistors along with a differential 10nF input capacitor.

Table 10-1 BOM for INA191A4EVM Modifications
Name (EVM Designator) Value Tolerance Drift (ppm/°C) Package
RSHUNT (R34) 1Ω 1% 200ppm/°C 1206
REXT1 (R74), REXT2 (R84) 2.2kΩ 1% 25ppm/°C 0603
CDIFF (C34) 10nF 5% C0G, NP0 0603

Input-Output sweeps were run on the EVM at -40°C, 25°C, and 125°C ambient temperatures first with REXT = 0Ω and then with REXT = 2.2kΩ. Load current was controlled by a power rheostat and monitored a precision, 8-digit Ammeter. Approximate current sweep range was from 0.48µA to 240mA. VOUT was measured by a >5.5 -digit voltmeter and monitored to remain with device's linear output operating region. Linear output region for INA191 was defined at 0.9V < VOUT < 4.9V.

Data analysis began by calculating the total shunt voltage gain using a 2-point line method on all of the VOUT and the VDIFF values within the designated linear output region. For each VDIFF, an input offset is calculated using linear interpolation with the calculated gain. The final VOS chosen for analysis was the average of all individual offsets pertaining to designated linear output region. Data analysis using gain calculated from a best-fit line was also performed as a check for any major dissimilarities.

Exact external input resistance errors (EG, EXT, VOS, EXT, EG DRIFT, EXT, VOS Drift, EXT) quantified by simply calculating the error difference with and without input resistances. Note that the same eEXT error can be calculated even if shunt resistor was not calibrated.