UCS1601SG-S08-R datasheet(5/8 Pages) UTC

5 / 8 page

UCS1601S

Preliminary

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

5 of 8

www.unisonic.com.tw

QW-R103-119.a



FUNCTIONAL DESCRIPTION

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 inter-slope voltage VSOFTS and VCS on

current sense resistor at beginning. After the whole soft-start phase end, and driver duty cycle depend on VFB and

VCS. The relation among VSOFTS, 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.

Fig.3 Soft-start phase

(2) Internal Synchronized Slope Compensation

Built-in slope compensation circuit adds voltage ramp onto the current sense input voltage for PWM generation,

this greatly improves the close loop stability at CCM and prevents the sub-harmonic oscillation and thus reduces the

output ripple voltage.

(3) Frequency Hopping For EMI Improvement

The Frequency Hopping is implemented in the IC; there are two oscillators built-in the IC. The first oscillator is to

set the normal switching frequency; the switching frequency is modulated with a period signal generated by the 2nd

oscillator. The relation between the first oscillator and the 2nd oscillator as followed Fig.4. So the tone energy is

evenly spread out, the spread spectrum minimizes the conduction band EMI and therefore eases the system design

in meeting stringent EMI requirement.

Fig.4 Frequency Hopping

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