TIDUF65 March   2024

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Consideration
    3. 2.3 Highlighted Products
      1. 2.3.1 TMCS1123
      2. 2.3.2 ADS7043
      3. 2.3.3 AMC1035
      4. 2.3.4 REF2033
  9. 3System Design Theory
    1. 3.1 Hall-Effect Current Sensor Schematic Design
    2. 3.2 Analog-to-Digital Converter
      1. 3.2.1 Delta-Sigma Modulator
        1. 3.2.1.1 Common-Mode Voltage Limit
        2. 3.2.1.2 Input Filter
        3. 3.2.1.3 Interface to MCU
      2. 3.2.2 12-bit SAR ADC
        1. 3.2.2.1 Common-Mode Voltage Limit
        2. 3.2.2.2 Input Filter
        3. 3.2.2.3 Interface to MCU
    3. 3.3 Power Supply and Reference Voltage
  10. 4Hardware, Software, Testing Requirements, and Test Results
    1. 4.1 Hardware Requirements
    2. 4.2 Software Requirements
    3. 4.3 Test Setup
      1. 4.3.1 Precautions
    4. 4.4 Test Results
      1. 4.4.1 DC Performance
        1. 4.4.1.1 Output Voltage Noise and ENOB After A/D Conversion
        2. 4.4.1.2 Linearity and Temperature Drift
      2. 4.4.2 AC Performance
        1. 4.4.2.1 SNR Measurement
        2. 4.4.2.2 Latency Test
      3. 4.4.3 PWM Rejection
      4. 4.4.4 Overcurrent Response
      5. 4.4.5 Adjacent Current Rejection
      6. 4.4.6 Power Supply Rejection Ratio
      7. 4.4.7 Digital Interface
  11. 5Performance Comparison with Competitor’s Device
    1. 5.1 Effective Number of Bits
    2. 5.2 Latency
    3. 5.3 PWM Rejection
  12. 6Design and Documentation Support
    1. 6.1 Design Files
      1. 6.1.1 Schematics
      2. 6.1.2 BOM
      3. 6.1.3 PCB Layout Recommendations
        1. 6.1.3.1 Layout Prints
    2. 6.2 Tools and Software
    3. 6.3 Documentation Support
    4. 6.4 Support Resources
    5. 6.5 Trademarks
  13. 7About the Author

3.1 Hall-Effect Current Sensor Schematic Design

The TMCS1123 offers ±1300V reinforced working voltage with ≥ 8mm clearance and creepage. The zero-current output for TMCS1123Bx, when supplied with 3.3V is 1.65V so it is intended for bidirectional current sensing with a unipolar full-scale analog output from 0V to 3.3V. The TMCS1123Bx variants differ in sensitivity and support a wide current measurement range from ±10.3A to ±62A, with a 3.3V supply.

GUID-20240216-SS0I-ZT6Q-XFRW-1PNJ3D1HBQT8-low.svg Figure 3-1 Hall Sensor TMCS1123 Schematic

In this reference design, TMCS1123B1 is used for DC and AC noise tests, the B3 version is used for noise immunity, overcurrent detection and latency tests. For the B1 version, the sensitivity is 25mV/A and the linear input current range is ±62A. For the B3 version, the sensitivity is 75mV/A and the linear input current range is ±20.7A. The VREF pin outputs a constant 1.65V, and can be connected to the negative input of ADC and form a pseudo-differential input which helps improve the immunity to noise.

Both OC and FAULT pin are open-drain output, so a pullup resistor is needed. In this design, the OC pin and FAULT pin are connected to the 3.3V supply through a 10kΩ pullup resistor. For the OC pin the Schmitt trigger SN74LVC1G17 is used to filter out the noise and avoid a false trigger, R19 and C15 blank the noise and default delay td can be calculated using Equation 1:

Equation 1. t d = R 19 C 15 = 1 μ s

VOC is used for overcurrent detection threshold setting. VOC can be calculated with Equation 2:

Equation 2. V O C = S × I O C 2 . 5

where

  • S is sensitivity of the Hall sensor. For TMCS1123B1, S = 25mV/A, For TMCS1123B3, S = 75mV/A
  • IOC is the overcurrent threshold.

To set a 40A threshold, VOC needs to be 1.2V.

The resistor divider R22 and R23 can be calculated with Equation 3:

Equation 3. R 23 R 22 + R 23 = V O C V s

Select 7.87kΩ as R23, R22 needs to be 13.77kΩ.