U3848 Datasheet, PDF (7/12 Pages) Unisonic Technologies – HIGH PERFORMANCE CURRENT MODE PWM CONTROLLERS

UC3848
LINEAR INTEGRATED CIRCUIT

„ FUNCTIONAL DESCRIPTION(Cont.)

(3) Protection section
UC3848 takes on more protection functions such as OLP, OVP and OTP etc. In case of those failure modes for
continual 7.2µs (blanking time), the driver is shut down. At the same time, IC enters auto-restart, V_CC power on and
driver is reset after V_CC power on again.
OLP
After soft-start phase end (V_SS>5.1V), IC will shutdown driver if over load state occurs (corresponding to
V_FB>4.6V) for continual 7.2µs. OLP function will not inactive during soft-start phase. OLP case as followed FIG.6.
The test circuit as followed FIG.8.




FIG.6 OLP case
FIG.7 OVP case
OVP
Power supply V_CC’s OVP function are enabled only when V_SS<3.9V & V_FB>4.6V during soft-start phase. During
above condition, driver will be shutdown if over voltage state occurs (V_CC>16V) for continual 7.2µs. OVP function will
not inactive after soft-start phase. OLP case as followed FIG.7. The test circuit as followed FIG.9.
OTP
OTP will shut down driver when junction temperature T_J of internal circuits is more than threshold 135°C for
continual 7.2µs.
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
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QW-R103-033,C