35.1 External Resistor Selection

The ZCD module requires a current-limiting resistor in series with the external voltage source. The impedance and rating of this resistor depends on the external source peak voltage. Select a resistor value that will drop all of the peak voltage when the current through the resistor is nominally 300 μA. Make sure that the ZCD I/O pin internal weak pull-up is disabled so it does not interfere with the current source and sink.

Equation 35-1. External Resistor

R_{S E R I E S} = \frac{V_{P E A K}}{3 \times 10^{- 4}}