US1702 datasheet(4/5 Pages) UTC

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US1702

Preliminary

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

4 of 5

www.unisonic.com.tw

QW-R911-020.c



FUNCTIONAL DESCRIPTION

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

(1) High Voltage Start up switch Circuit

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

connected to the VCC pin. When VCC reaches VTHD (ON), the IC begins switching and the internal high-voltage current

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

transformer winding unless VCC goes below the stop voltage of VCC(MIN).

(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

continual blanking time, the driver is shut down. At the same time, IC enters auto-restart, VCC power on and driver is

reset after VCC power on again.

OVP

OVP will shutdown the switching of the power MOSFET whenever VCC>VOVP. The OVP case as followed Fig. 1

the test circuit as followed Fig. 2.

UTC

US1702

470u

33n

IC3

VCC

15V

VCC

Drain

VOVP

470u

33n

VDD

15V

500Ω

Fig.1 OVP case

Fig.2 OVP test circuit

OTP

OTP will shut down driver and latch-off when junction temperature TJ>T (THR), and IC will be release on when

temperature decreasing under T (THR)-30 and powering on again.

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

ILIM=GFB-D×0.23V×(R2||R1)

(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.

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