This section describes a typical three-phase energy measurement front-end using the AMC131M01. The ADC samples the outputs of resistive current sensors (shunts) to measure the current of each leg of the AC mains. The design can achieve high accuracy across a wide input current range (0.05 A–100 A) and supports high sampling frequencies necessary for advanced power-quality features, such as individual harmonic analysis. Using the AMC131M01 to sample the currents per phase provides designers greater flexibility in the choice of metrology microcontrollers (MCU) when compared to an integrated system-on-a-chip (SoC) and dedicated application-specific products.

Figure 9-4 illustrates the front-end for a three-phase energy measurement design. In this design, one AMC131M01 per phase measures the current for this respective phase, providing galvanic isolation from phase to phase. This isolation is critical because the voltage level in a typical case can be in the order of 220 V on one phase and –220 V at another phase. If only one ADC for multiple phases is used, a voltage difference in the order of 440 V between two adjacent ADC inputs can appear, potentially destroying the device.

The measurement of each phase voltage is implemented either using the on-board ADCs of the MCU as shown in Figure 9-4, or a discrete, multichannel, non-isolated ADC. The high voltage from the individual phase is scaled down using a resistive divider for each voltage measurement.

RC antialiasing filters are not given in Figure 9-4 for simplicity, but are recommended for all channels.

The microcontroller uses the SPI port to communicate with the three ADC devices, and provides a clock to all ADC devices at the respective CLKIN pins. Three of the microcontroller I/O pins (CS_A, CS_B, and CS_C) generate the SPI CS signals. The SCLK, DIN, and DOUT connections are shared between all ADC devices. To simplify the figure, these connections are not shown in detail.

Figure 9-4 3-Phase Metrology Design Front-End Using the AMC131M01