L8565

Preliminary

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

7 of 13

www.unisonic.com.tw

QW-R114-004.d



FUNCTIONAL DESCRIPTION(Cont.)

3. Start-up (Soft-Start)

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

(

)

R4

R3+R4

10.8μA during

Soft Start

R6

C4

C5

UTC L8565

0.8V

C3

-

+

S1

5V

-

+

OTA1

Soft Start

4.0V

Fig. 4 Soft Start Circuit

Soft Start

Normal Operation

t

Fig. 5 Soft Start With Controlled Current

Open-Loop

Protect

(OLP)

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

shown in Fig. 6 and 7.

The following sections describe the functionality of these protection features.