Live Voltage Sense Inputs

Live voltages are connected to two positions in the same connector (J2). These lines are connected to the inputs of the A/D converter through a resistor divider with a ratio of 0.6057V/1000V. The TCR of the resistors is 25 ppm/ºC.

The two inputs (L1 and L2) have the same resistor divider schematic and layout. The metering ground reference, GND, is connected to the Line Voltage input VN.
Important: The resistors installed by default in the divider (ratio of 0.6057V/1000V) allow a maximum input voltage of 291 Vrms. It is recommended that the divider ratio be reduced to be able to measure higher input voltage values. Also, take into account the AC power supply input range (from 90 to 264 Vac and from 47 to 63 Hz). If this range is not accomplished, removing the AC power supply (U1) is required to not damage it.
Figure 1. Lines Voltage Sense Schematic
An anti-aliasing filter is required for band-limiting the input signals. Typically, a single-pole RC filter is sufficient for metrology applications. The filter is tuned with the following component values:
Some test points close to the resistor dividers allow monitoring the input voltage value at the A/D converter inputs:
Figure 2. VP1 and VP2 Test Points