BM1Q021FJ Datasheet, PDF (18/31 Pages) Rohm – Quasi-Resonant Control type

BM1Q021FJ/BM1Q041FJ
Datasheet
(4-6) ZT Trigger Mask Function（Figure-22）
When switching is set from ON to OFF, superposition of noise may occur at the ZT pin.
Then, the ZT comparator and ZTOVP comparator are masked for the T_ZTMASK time to prevent ZT comparator operation errors.
Figure-21 ZT Trigger Mask Function
A: DC/DC OFF=>ON
B: DC/DC ON=>OFF then the surge noise occurs to ZT pin.
C: Since a noise occurs to ZT pin at B, IC masks ZT comparator and ZTOVP comparator detection for T_ZTMASK time.
(4-7-1) ZT Timeout Function1 （Figure-23）
When ZT pin voltage is not higher than V_ZT2(typ=200mV) for T_ZTOUT1(typ=15us) such as start or low output voltage, ZT pin short,
IC turns on MOSFET by force.
(4-7-2) ZT Timeout Function2 （Figure-23）
After ZT comparator detects bottom, when IC does not detect next bottom within T_ZTOUT2（typ =5us）, IC turns on MOSFET
by force. After ZT comparator detects bottom at once, the function operates. For that, it does not operate at start or at low output
voltage. When IC is not able to detect bottom by decreasing auxiliary winding voltage, the function operates.
V_ZT2
ZT V_ZT1
ZT pin GND
short
Bottom
detection
5us
timeout
5us
5us
15us
15us
15us
timeout
CS
OUT
A
BC
DE
F GH
I
Figure-22 ZT Timeout Function
A: When starting, IC starts to operate by ZT timeout function1 for ZT=0V.
B: MOSFET turns ON
C: MOSFET turns OFF
D: ZT voltage is lower than V_ZT2(typ=200mV) by ZT dump decreasing.
E: MOSFET turns ON by ZT timeout fucntion2 after T_ZTOUT2(typ=5us) from D point.
F: ZT voltage is lower than V_ZT2(typ=200mV) by ZT dump decreasing.
G: MOSFET turns ON by ZT timeout fucntion2 after T_ZTOUT2(typ=5us) from F point.
H: ZT pin is short to GND.
I : MOSFET turns ON by ZT timeout function1 after T_ZTOUT1(typ=15us)
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TSZ22111・15・001
18/27
TSZ02201-0F1F0A200280-1-2
27.Sep.2016 Rev.001