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BM2PXX2F
(7) SOURCE pin short protection function
When the SOURCE pin is shorted, BM2PXX2F is over heat.
BM2PXX2F built in short protection function to prevent destroying.
(8) SOURCE pin open protection
If the SOURCE pin becomes OPEN, BM2PXX2F may be damaged.
To prevent to be damaged, BM2PXX2F built in OPEN protection circuit（auto recovery protection）.
(9) Output over load protection function （FB OLP Comparator）
The output overload protection function monitors the secondary output load status at the FB pin, and stops switching when
an overload occurs. In case of an overload, the output voltage is reduced and current no longer flows to the photo coupler,
so the FB pin voltage rises.
When the FB pin voltage > VFOLP1A (2.8 V typ) continuously for the period TFOLP1 (64ms typ), it is judged as an overload and
stops switching.
When the FB pin > VFOLP1A (2.8 V typ), if the voltage goes lower than VFOLP1B (2.6V typ) during the period TFOLP1 (64ms typ),
the overload protection timer is reset. The switching operation is performed during this period TFOLP1 (64ms typ).
At startup, the FB voltage is pulled up to the IC’s internal voltage, so operation starts at a voltage of VFOLP1A (2.8 V typ) or
above. Therefore, at startup the FB voltage must be set to go to VFOLP1B (2.6 V typ) or below during the period TFOLP1 (64ms
typ), and the secondary output voltage’s start time must be set within the period TFOLP1 (64ms typ) following startup of the IC.
Recovery from the once detection of FBOLP, after the period TFOLP2 (512 ms typ)
Figure 15. Over load protection (Auto recovery)
A: The FBOLP comparator detects over load for FB>VFOLP1A
B: If the State of A continues for the period TFOLP1 (64ms typ), it is judged as an overload and stops switching after 64ms.
C: While switching stops for the over load protection function, the VCC pin voltage drops and VCC pin voltage reaches <
VCHG1, the VCC charge function operates so the VCC pin voltage rises.
D: VCC charge function stops when VCC pin voltage > VCHG2
E: If TFOLP2 （typ =512ms） go on from B point, Switching function starts on soft start.
F: If TFOLP1 (64ms typ) go on from E point to continues an overload condition (FB>VFOLP1A), Switching function stops
at F point.
G: While switching stops VCC pin voltage drops to < VCHG1, VCC charge function operates and VCC pin voltage rises.
H: If VCC pin (1pin) voltage becomes over VCHG2 by the VCC charge function, VCC charge function operation stops.
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TSZ02201-0F2F0A200040-1-2
7. Mar.2017.Rev.007
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TSZ22111・15・001
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