TIDUFB8 December   2024

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Key System Specifications
    2. 1.2 End Equipment
    3. 1.3 Electricity Meter
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Voltage Measurement – Analog Front End
      2. 2.2.2 Current Measurement Analog Front End
      3. 2.2.3 Input Voltage
      4. 2.2.4 Clock
    3. 2.3 Highlighted Products
      1. 2.3.1 AMC130M02
      2. 2.3.2 MSPM0G1106
      3. 2.3.3 LMK6C
      4. 2.3.4 TLV76133
  9. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
    2. 3.2 Software Requirements
      1. 3.2.1 Formulas
      2. 3.2.2 Metrology Software Process
        1. 3.2.2.1 UART for PC GUI Communication
        2. 3.2.2.2 Direct Memory Access (DMA)
        3. 3.2.2.3 ADC Setup
        4. 3.2.2.4 Foreground Process
        5. 3.2.2.5 Background Process
        6. 3.2.2.6 Software Function per_sample_dsp ()
        7. 3.2.2.7 Frequency Measurement and Cycle Tracking
        8. 3.2.2.8 LED Pulse Generation
    3. 3.3 Test Setup
      1. 3.3.1 Power Supply and Jumper Settings
      2. 3.3.2 Viewing Metrology Readings and Calibration
      3. 3.3.3 Calibration
        1. 3.3.3.1 Voltage and Current Offset Calibration
        2. 3.3.3.2 Voltage and Current Gain Calibration
        3. 3.3.3.3 Active Power Gain Calibration
        4. 3.3.3.4 Offset Calibration
        5. 3.3.3.5 Phase Calibration
    4. 3.4 Test Results
      1. 3.4.1 Electricity Meter Metrology Accuracy Results
  10. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
      3. 4.1.3 PCB Layout Recommendations
        1. 4.1.3.1 Layout Prints
      4. 4.1.4 Altium Project
      5. 4.1.5 Gerber Files
      6. 4.1.6 Assembly Drawings
    2. 4.2 Tools and Software
    3. 4.3 Documentation Support
    4. 4.4 Support Resources
    5. 4.5 Trademarks
  11. 5About the Author

2.2.2 Current Measurement Analog Front End

Figure 2-3 shows how the current input analog front end is different from voltage analog front end.

TIDA-010960 Analog Front End for Current Input Figure 2-3 Analog Front End for Current Input

The analog front end for current consists of footprints for electromagnetic interference filter beads (FB6 and FB8), and a RC low-pass filter (R12, R21, C16, C18).

Equation 2 shows how to calculate the range of differential voltages fed to the current ADC channel for a given maximum current, and shunt resistor value.

Equation 2. V A D C S w i n g , C u r r e n t , S h u n t =   ±   2   R s h u n t   I R M S , m a x

A SHUNT value of 3mΩ is used, the input signal to the current ADC has a voltage swing of ±63.6mV, 63.6mV when the current rating of the meter (15A) is applied. This relatively low voltage, when using GAIN = 16 is well within the required Full-Scale Range of ±75mV. See also the full-scale range table in the AMC130M02 2-Channel, 64kSPS, Simultaneous-Sampling, 16-Bit, Reinforced Isolated Delta-Sigma ADC With Integrated DC/DC Converter data sheet.

Table 2-1 Full-Scale Range
GAIN SETTING FSR
1 ±1.2V
2 ±600mV
4 ±300mV
8 ±150mV
16 ±75mV
32 ±37.5mV
64 ±18.75mV
128 ±9.375mV