The Shunt Resistor technique uses a small (shunt) resistor placed in the path of the load current. When the load current flows through this resistance, a small voltage drop is developed across it. This voltage drop is measured by an input of the AFE, which converts it into the corresponding current consumption.
Figure 1. IPx and INx Current Sense
Schematic when Using Shunt
Warning: A shunt resistor must be
placed in series with the line to be measured, then connected to the measurement inputs.
The demonstration board is referred to neutral; therefore, a shunt resistor can only be
used in neutral line. Using a shunt resistor to measure currents in lines 1 or 2 will
damage the board, and it is dangerous for the user.
For Shunt operation, the input network must only provide a first-order low-pass filter.
The filter must be tuned with the following component values:
- RA1, RA2 = Do Not Populate
- RB1, RB2 = 0Ω
- RC1, RC2 = 3 kΩ, 1%, 25 ppm/ºC
- CA1, CA2 = 47 pF Y7R
- CB1, CB2 = Do Not Populate
- CC1, CC2 = 3.3 nF NP0/COG
- D1, D2 = Si Junction diodes (recommended)