MAP8802 Datasheet, PDF (13/16 Pages) MagnaChip Semiconductor. – CRM PFC Controller

12. ZCD Short Protection
Max Frequency Limit
This function prevents the operation of the CCM and
the burning of wires when the Aux short,(See Figure 26)
The initial operation starts with CCM mode because the
output voltage is lower than input. The CCM operation let
the switching frequency increase until output voltage
approaches the setting voltage. At this moment, the
frequency is over 2MHz. MAP8802 is designed to be
operated in critical conduction mode (CRM). However,
when Aux short occurs, IC cannot operate with CRM
mode because the ZCD voltage cannot be detected. At
this moment, the operation mode is CCM and frequency is
over 2MHz. Therefore, maximum frequency limit is
required because the high frequency is occurred the
burning of wire.
VAUX
Short
MP8802
8 VCC
Out 7
5 ZCD
CS 4
2 ^Ct
FB
3 Control
1
GND
6
Figure 26. Aux wire short
Off timer protection
If ZCD noise is not existed, MAP8802 is operating as off
timer (T-start timer) because ZCD signal is be absent.
But It is can be occurred audible noise because the
period is about 150us.(about 6Khz) To prevent audible
noise, MAP8802 detects the cycle of Tstart Timer. If
Tstart Timer reached 16cycle, MAP8802 entered Auto-
restart protection mode.
VCC
VCC(ON)
VCC(OFF)
Switching
current
Start-Up
ZCD Short Point
TSTART_Timer
TSTART Timer : 150us
150us ^TSTART ^{Timer : 16Cycle}
TSTART Timer : 150us
Ton Pulse width : 1u Sec.
Figure 27. ZCD off timer protection
Datasheet Version 1.3
AUG, 2015
MagnaChip Confidential Document. Do not distribute.