ON Semiconductor NCN49597 Manual page 17

ZC_IN
Zero Cross Detector
ZC_IN is the mains frequency analog input pin. The signal
is used to detect the zero cross of the 50 or 60 Hz sine wave.
This information is used, after filtering with the internal
PLL, to synchronize frames with the mains frequency. In
FROM
MAINS
1 MW
Figure 10. Zero Cross Detector with Falling Edge De−bounce Filter
The zero cross detector output is logic zero when the input
is lower than the falling threshold level and a logic one when
the input is higher than the rising threshold level. The falling
Clock and Control
Zero
PLL
crossing
PC20090619.4
Figure 9. Clock and Control Block
3V3_A
BAS70− 04
ZC_IN
100 pF
http://onsemi.com
NCN49597
Clock Generator
CHIP_CLK
& Timer
case of direct connection to the mains it is advised to use a
series resistor of 1 MW in combination with two external
Schottky clamp diodes in order to limit the current flowing
through the internal protection diodes.
Debounce
Filter
edges of the output of the zero cross detector are de−bounced
by a period between 0.5 ms and 1 ms. The Rising edges are
not de−bounced.
17
OSC
XIN XOUT
Clock & Control
ZeroCross
CHIP_CLK
PLL
PC20100608.1