8565L-S08-R datasheet(7/13 Pages) UTC

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8565

Preliminary

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

7 of 13

www.unisonic.com.tw

QW-R114-004.b

FUNCTIONAL DESCRIPTION(Cont.)

3. Start-up (Soft-Start)

The operation of OTA1 during startup is shown in Fig. 4 and 5.

VSENSE

(

)

R3+R4

×VOUT

10.8μA during

Soft Start

VCOMP

UTC 8565

0.8V

OTA1

Soft Start

4.0V

Fig. 4 Soft Start Circuit

Soft Start

Normal Operation

VOUT<80% rated

VOUT>80% rated

av(IIN)

Fig. 5 Soft Start With Controlled Current

Open-Loop

Protect

(OLP)

It sources a constant 10.8µA into the compensation network at pin 2 (VCOMP). The voltage at this pin rises

linearly and so does the amplitude of the input current. As soon as the output voltage VOUT reaches 80% of its rated

level, the startup procedure is finished and the normal voltage control takes over. In normal operation, the IC

operates with a higher maximum current at OTA1 and therefore with a higher voltage loop gain in order to improve

the dynamic behavior of the device.

The advantage of this technique is a soft-start function with lower stress for the boost diode but without the risk of

audible noise.

4. System Protection

The IC is equipped with various protection features to ensure the PFC system in safe operating range. Depending

on the input line voltage (VIN) and output bus voltage (VOUT), When these protections are active the conditions are

shown in Fig. 6 and 7.

The following sections describe the functionality of these protection features.

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