UPS604 Datasheet, PDF (6/12 Pages) Unisonic Technologies – HIGH PERFORMANCE CURRENT MODE POWER SWITCH

UPS604
LINEAR INTEGRATED CIRCUIT
„ FUNCTIONAL DESCRIPTION
The internal reference voltages and bias circuit work at V_CC> V_{THD (ON)}, and shutdown at V_CC<V_{CC (MIN)}.
(1) Soft-Start
When every IC power on, driver output duty cycle will be decided by voltage V_SS on soft-start capacitor and V_CS
on current sense resistor at beginning. After V_SS reach 4.2V, the whole soft-start phase end, and driver duty cycle
depend on V_FB and V_CS. The relation among V_SS, V_FB and V_OUT as followed FIG.3.
Furthermore, soft-start phase should end before V_CC reach V_{CC (MIN)} during V_CC power on. Otherwise, if soft-start
phase remain not end before V_CC reach V_{CC (MIN)} during V_CC power on, IC will enter auto-restart phase and not set up
V_OUT. So the value of C_SS should be between 0.1μFand 4.7μF.
Finally soft-start also set OVP1 active phase. OVP1 active phase between 0 and V_SS(DEACT), OVP1 will not be
sensed after V_SS reach V_SS(DEACT).The Soft-start phase T_SS：T_SS = 23.8×C_SS (ms) (Example: C_SS=0.47μF, then
T_SS=23.8×0.47=11.2ms).
V_SS
4.2V
T_SOFT-START
t
V_FB
4.8V
t
V_OUT
T_STRAT-UP
t
Driver
t
Fig.3 Soft-start phase
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QW-R119-006.E