SBOSAF3 November   2023 TMCS1126

ADVANCE INFORMATION  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison
  6. 5 Pin Configuration and Functions
  7. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Insulation Specifications
    6. 6.6 Electrical Characteristics
  8. 7 Parameter Measurement Information
    1. 7.1 Accuracy Parameters
      1. 7.1.1 Sensitivity Error
      2. 7.1.2 Offset Error and Offset Error Drift
      3. 7.1.3 Nonlinearity Error
      4. 7.1.4 Power Supply Rejection Ratio
      5. 7.1.5 Common-Mode Rejection Ratio
      6. 7.1.6 External Magnetic Field Errors
    2. 7.2 Transient Response Parameters
      1. 7.2.1 CMTI, Common-Mode Transient Immunity
    3. 7.3 Safe Operating Area
      1. 7.3.1 Continuous DC or Sinusoidal AC Current
  9. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Current Input
      2. 8.3.2 Input Isolation
      3. 8.3.3 Ambient Field Rejection
      4. 8.3.4 High-Precision Signal Chain
        1. 8.3.4.1 Temperature Stability
        2. 8.3.4.2 Lifetime and Environmental Stability
      5. 8.3.5 Internal Reference Voltage
      6. 8.3.6 Current-Sensing Measurable Ranges
      7. 8.3.7 Overcurrent Detection
    4. 8.4 Device Functional Modes
      1. 8.4.1 Power-Down Behavior
  10. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Total Error Calculation Examples
        1. 9.1.1.1 Room-Temperature Error Calculations
        2. 9.1.1.2 Full-Temperature Range Error Calculations
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
    3. 9.3 Power Supply Recommendations
    4. 9.4 Layout
      1. 9.4.1 Layout Guidelines
      2. 9.4.2 Layout Example
  11. 10Device and Documentation Support
    1. 10.1 Device Support
      1. 10.1.1 Development Support
    2. 10.2 Documentation Support
      1. 10.2.1 Related Documentation
    3. 10.3 Receiving Notification of Documentation Updates
    4. 10.4 Support Resources
    5. 10.5 Trademarks
    6. 10.6 Electrostatic Discharge Caution
    7. 10.7 Glossary
  12. 11Revision History
  13. 12Mechanical, Packaging, and Orderable Information
    1. 12.1 Package Option Addendum
    2. 12.2 Tape and Reel Information

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9.2.2 Detailed Design Procedure

The primary design parameter for using the TMCS1126 is the optimum sensitivity variant based on the required measured current levels and the selected supply voltage. Positive and negative currents are measured in this in-line phase current application example, therefore select a bidirectional variant. The TMCS1126 has a precision internal reference voltage that determines the zero current output voltage, VOUT,0A. The internal reference voltage on TMCS1126Axx variants, with zero current output voltage VOUT,0A = 2.5 V is intended for bidirectional current measurements when used with 5-V power supplies. The internal reference voltage on TMCS1126Bxx variants, with zero current output voltage VOUT,0A = 1.65 V is intended for bidirectional current measurements when used with 3.3-V power supplies. Further consideration of noise and integration with an ADC can be explored, but is beyond the scope of this application design example. The TMCS1126 output voltage VOUT is proportional to the input current IIN as defined by Equation 29 with output offset set by VOUT,0A.

Equation 29. VOUT=IIN×S+VOUT,0A

Design of the sensing solution focuses on maximizing the sensitivity of the device while maintaining linear measurement over the expected current input range. The TMCS1126 has a slightly smaller linear output range to the supply than to ground, therefore the measurable current range is always constrained by the positive swing to supply, SwingVS. To account for the operating margin, consider the minimum possible supply voltage VS,min. With the previous parameters, the maximum linear output voltage VOUT,max is defined by Equation 30.

Equation 30. VOUT,max=VS,min-SwingVS

Design parameters for this example application are shown in Table 9-4 along with the calculated output range.

Table 9-4 Example Application Design Parameters
DESIGN PARAMETEREXAMPLE VALUE
SwingVS0.1 V
VOUT,max4.8 V
VOUT,0A2.5 V
VOUT,max – VOUT,0A2.3 V

These design parameters result in a maximum positive linear output voltage swing of ±2.3 V about VOUT,0A = 2.5 V. To determine which sensitivity variant of the TMCS1126 most fully uses this linear range, use Equation 31 to calculate the maximum current range for a bidirectional current ±IIN,max.

Equation 31. IIN, max=VOUT,max-VOUT,0AS

where

  • S is the sensitivity of the relevant AxA variant.

Table 9-5 shows the calculation for each gain variant of the TMCS1126 with the appropriate sensitivities.

Table 9-5 Maximum Full-Scale Current Ranges With 2.3-V Positive Output Swing
VARIANTSENSITIVITYIIN,max
TMCS1126A1x25 mV/A±92 A
TMCS1126A2x50 mV/A±46 A
TMCS1126A3x75 mV/A±30.6 A
TMCS1126A4x100 mV/A±23 A
TMCS1126A5x150 mV/A±15.3 A

In general, the highest sensitivity variant is selected to provide the lowest maximum input current range that is larger than the desired full-scale current range. For the design parameters in this example, either the higher precision TMCS1126A4Aor the less accurate TMCS1126A4B (both with sensitivity of 0.1 V/A) is the proper selection because the maximum ±23A linear measurable range is larger than the desired ±20A full-scale current range.