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 System Design Theory

Hall-effect current sensors like the TMCS1123 offer several advantages over shunt-based designs for reinforced isolated current sensing and overcurrent detection in 3-phase inverters. There is no need for a shunt or for an isolated bias supply, thus reducing system cost and PCB space. Another advantage is the very low analog signal propagation delay of 600ns (TMCS1123), and fast overcurrent detection (<0.5μs), where the overcurrent threshold can be up to 2.5-times the full-scale input current range.

Table 3-1 Brief Comparison of Isolated Semiconductor Current Sensing Designs
PARAMETER TMCS1123 AMC1300 AMC1306M05 AMC23C11
Description Hall-effect sensor Isolated amplifier Isolated modulator Isolated comparator
ENOB (TYP) ≤ 10(1) ≤ 11 > 12(2) N/A
Propagation delay 0.6μs 1.7μs 4.8μs(2) N/A
Interface Analog Analog Digital Digital
Isolated supply required No Yes Yes Yes
OC response time 0.1μs 2.4μs 1.2μs(3) 300ns
(1) ENOB typically depends on the full-scale range, see Table 3-2
(2) With Sinc3 OSR 64 decimation filter
(3) With Sinc3 OSR 8 decimation filter

Other than shunt-based designs, the signal-to-noise ratio with in-package Hall-effect sensors scale with the full-scale current range of the Hall sensors, since the input referred noise density is independent of the device sensitivity and therefore, the input current range. Table 3-2 outlines the calculated ENOB over the full-scale range of the device with a 250kHz cutoff frequency, and a brick-wall factor of 1.22 to estimate the effective noise bandwidth.

Table 3-2 Estimated ENOB With TMCS1123 Device Variants
PARAMETER TMCS1123B1A TMCS1123B2A TMCS1123B3A
Input Noise Density 170μA/√Hz 170μA/√Hz 170μA/√Hz
FSR (MAX) ±66A ±33A ±22A
SNR (DC) 57dB 51dB 47dB
ENOB (DC) 9.2 8.2 7.6