SBOSA80 December   2021 REF20-Q1

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Typical Characteristics
  8. 8 Parameter Measurement Information
    1. 8.1 Solder Heat Shift
    2. 8.2 Long-Term Stability
    3. 8.3 Thermal Hysteresis
    4. 8.4 Noise Performance
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 VREF and VBIAS Tracking
      2. 9.3.2 Low Temperature Drift
      3. 9.3.3 Load Current
    4. 9.4 Device Functional Modes
  10. 10Applications and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Low-Side, Current-Sensing Application
        1. 10.2.1.1 Design Requirements
        2. 10.2.1.2 Detailed Design Procedure
          1. 10.2.1.2.1 Shunt Resistor
          2. 10.2.1.2.2 Differential Amplifier
          3. 10.2.1.2.3 Voltage Reference
          4. 10.2.1.2.4 Error Calculations
          5. 10.2.1.2.5 Application Curves
  11. 11Power-Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Documentation Support
      1. 13.1.1 Related Documentation
    2. 13.2 Receiving Notification of Documentation Updates
    3. 13.3 Support Resources
    4. 13.4 Trademarks
    5. 13.5 Electrostatic Discharge Caution
    6. 13.6 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information
10.2.1.2.4 Error Calculations

Two types of errors will be discussed: initial accuracy and drift. Accuracy errors include:

  • Shunt resistor tolerance: αshunt_tol = 0.1% (maximum)
  • INA initial input offset voltage: VOS_INA = 5 μV (typical)
  • INA PSRR: VOS_INA_PSRR = 1 μV/V (typical)
  • INA CMRR: VOS_INA_CMRR = 132 dB (typical)
  • INA gain error: αINA_GE = 0.05% (typical)
  • Reference output accuracy: αREF_output = 0.05% (maximum)

It should be noted that these error sources can be greatly reduced at 25ºC by performing a two point system calibration. Drift errors, on the other hand, can only be reduced by performing the calibration over temperature. The drift errors include:

  • Shunt resistor drift: δshunt_drift = 15 ppm/ºC (maximum)
  • INA offset voltage drift: δINA_drift_Vos = 50 nV/ºC (typical)
  • INA gain error drift: δINA_drift_GE = 0.5 ppm/ºC (typical)
  • Reference output drift: δREF_drift_output = 3 ppm/ºC (typical)

Equation 8 can be used to convert specifications given in parts per million (ppm) to a percentage (%), and vice versa.

Equation 8. % = (ppm/10,000)

Equation 9 can be used to convert specifications given in decibels (dB) to a linear representation.

Equation 9. (V / V) = (1 / 10(dB/20))

For some error calculations a full-scale range (FSR) is required. The FSR for this design is determined by the voltage across the shunt resistor, which is ±25 mV (or 50 mV).

For drift errors, the largest change in temperature (ΔT) is 100ºC, which is the difference between the maximum specified temperature (125ºC) and room temperature (25ºC). This temperature change is used when calculating drift errors for the shunt resistor and INA240-Q1. Because the REF20-Q1 uses the box method to determine drift, the temperature range used for calculations is the entire operating range, or 150ºC.

Finally, errors due to CMRR and PSRR specifications require an adjustment depending on the difference between the system’s requirements and how the devices were characterized. For example, the INA240-Q1 was characterized using a common-mode voltage of 12 V. The common-mode voltage in this design is ~0V. This discrepancy causes an input-referred offset voltage.

Below, Table 10-1 summarizes the initial accuracy calculations.

Table 10-1 Initial Accuracy Error Summary
ERROR SOURCE DEVICE: RSHUNT (PPM) DEVICE: IN240-Q1 (PPM) DEVICE: REF2030-Q1 (PPM) TOTAL (PPM, RSS)
OFFSET 100 FSR 500 FSR 510 FSR
CMRR 60 FSR 60 FSR
PSRR 40 FSR 40 FSR
GAIN ERROR 1000 500 1118
TOTAL (PPM, RSS) 1000 1087.5 FSR 500 FSR 1231 FSR
(0.123%)

Below, Table 10-2 summarizes the total temperature drift calculations.

Table 10-2 Temperature Drift Error Summary
ERROR SOURCE DEVICE: RSHUNT (PPM) DEVICE: IN240-Q1 (PPM) DEVICE: REF2030-Q1 (PPM) TOTAL (PPM, RSS)
OFFSET DRIFT 100 FSR 495 505 FSR
GAIN ERROR DRIFT 1500 50 1501
TOTAL (PPM, RSS) 1500 111.8 FSR 495 1583.52 FSR
(0.194%)