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| US1702_15 Datasheet, PDF (4/5 Pages) Unisonic Technologies – HIGH PERFORMANCE CURRENT MODE POWER SWITCH | |||
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US1702
Preliminary
LINEAR INTEGRATED CIRCUIT
ï® 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.
15V VCC
15V VDD
470u 33n
IC3
500Ω
1
8
2
7
UTC
US1702
3
6
470u 33n
Drain
4
5
VOVP
VCC
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-DÃ0.23VÃ(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 driverâs 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 âPower MOSFET SECTIONâ in electrical characteristics table.
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
4 of 5
QW-R911-020.c
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