US1702

Preliminary

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

4 of 5

www.unisonic.com.tw

QW-R911-020.c



FUNCTIONAL DESCRIPTION

(1) High Voltage Start up switch Circuit

At startup, an internal high-voltage current source supplies the internal bias and charges the external capacitor

source is disabled. The IC continues its normal switching operation and the power is supplied from the auxiliary

(2) Switching Frequency Limit

The UTC US1702 have a constant switching frequency of 60kHz.

(3) Protection section

The IC takes on more protection functions such as OVP and OTP etc. In case of those failure modes for

OVP

the test circuit as followed Fig. 2.

UTC

US1702

470u

2

1

3

4

7

8

6

5

33n

IC3

15V

Drain

470u

33n

15V

500Ω

Fig.1 OVP case

Fig.2 OVP test circuit

OTP

(4) The Gain of FB pin to Drain Current Limiting

(5) Driver Output Section

The driver-stage drives the gate of the MOSFET and is optimized to minimize EMI and to provide high circuit

efficiency. This is done by reducing the switch on slope when reaching the MOSFET threshold. This is achieved by a

slope control of the rising edge at the driver’s output. The output driver is clamped by an internal 15V Zener diode in

order to protect power MOSFET transistors against undesirable gate over voltage.

(6) Inside Power MOSFET

Specific Power MOSFET parameter is as “Power MOSFET SECTION” in electrical characteristics table.