SLVUDF6 September 2025
2.1.2.1 Voltage Measurement - Analog Front End
The nominal voltage from the mains in many regions of the world varies from 100V to 240V, so the voltage needs to be scaled down to be sensed by an ADC. Figure 2-2 shows the analog front end for the voltage scaling.
Figure 2-2 Analog Front End for Voltage InputThe analog front end for voltage input has a voltage divider network (R4, R5, R6, R8), and RC low-pass filter (R9, R11, C7, C9, and C8).
If offset calibration is not performed, the voltage-to-current crosstalk affects active energy accuracy much more than voltage accuracy when the current is low. To maximize the accuracy at lower currents, in this design the entire ADC range is not used for the voltage channel. The reduced ADC range for the voltage channels in this design still provide more than enough accuracy for measuring voltage. Equation 1 shows how to calculate the range of differential voltages fed to the voltage ADC channel for a given Mains voltage and selected voltage divider resistor values.
Based on this formula and selected resistor values in Figure 2-2, for a main voltage of 230V, the input signal to the voltage ADC has a voltage swing of ±246mV (174mVRMS). The ±246mV voltage ranges are well within the AMC130M02's input range.