34.2 Overview

The Zero-Cross Detector (ZCD) detects when an alternating voltage crosses through a threshold voltage near the ground potential. The threshold is the zero-cross reference voltage, Z_CPINV, and the typical value can be found in the Electrical Specifications section of the peripheral.

The connection from the ZCD input pin (ZCIN) to the alternating voltage must be made through a series current-limiting resistor (R_SERIES). The ZCD applies either a current source or sink to the ZCD input pin to maintain a constant voltage on the pin, thereby preventing the pin voltage from forward biasing the ESD protection diodes in the device. When the applied voltage is greater than the reference voltage, the ZCD sinks current. When the applied voltage is less than the reference voltage, the ZCD sources current.

The ZCD can be used when monitoring an alternating waveform for, but not limited to, the following purposes:

• Period measurement
• Accurate long-term time measurement
• Dimmer phase-delayed drive
• Low-EMI cycle switching