UC3848 데이터 시트보기 (PDF) - Unisonic Technologies

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UC3848

HIGH PERFORMANCE CURRENT MODE CONTROLLERS

Unisonic Technologies 

UC3848

„ FUNCTIONAL DESCRIPTION

LINEAR INTEGRATED CIRCUIT

The internal reference voltages and bias circuit work at VCC> VTHD (ON), and shutdown at VCC<VCC (MIN).

(1) Soft-Start

When every IC power on, driver output duty cycle will be decided by voltage VSS on soft-start capacitor and VCS

on current sense resistor at beginning. After VSS reach 4.2V, the whole soft-start phase end, and driver duty cycle

depend on VFB and VCS. The relation among VSS, VFB and VOUT as followed FIG.3.

Furthermore, soft-start phase should end before VCC reach VCC (MIN) during VCC power on. Otherwise, if soft-start

phase remain not end before VCC reach VCC (MIN) during VCC power on, IC will enter auto-restart phase and not set up

VOUT. So the value of CSS should be between 0.1μFand 4.7μF.

Finally soft-start also set OVP1 active phase. OVP1 active phase between 0 and VSS(DEACT), OVP1 will not be

sensed after VSS reach VSS(DEACT).The Soft-start phase TSS：TSS = 23.8×CSS (ms) (Example: CSS=0.47μF, then

TSS=23.8×0.47=11.2ms).

FIG.3 Soft-start phase

UNISONIC TECHNOLOGIES CO., LTD

www.unisonic.com.tw

5 of 11

QW-R103-033.F

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