SC1109 데이터 시트보기 (PDF) - Semtech Corporation
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SC1109 Datasheet PDF : 17 Pages
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PRELIMINARY - October 16, 2000
SYNCHRONOUS PWM CONTROLLER WITH
DUAL LOW DROPOUT REGULATOR
CONTROLLERS
SC1109
OVER CURRENT
Upper Mosfet’s Rdson is used to monitor the drop
across the top FET due to an over current condition.
This Method of current sensing minimizes any unnec-
essary losses due to external sense resistance.
An internal comparator with a 200mV reference moni-
tors the Drop across the upper FET, Once the Vdson
of the Mosfet exceeds the 200mV limit, the low side
gate is turned on and the upper FET is turned off.
Also an internal latch is set and the Soft start capaci-
tor is discharged. Once the lower threshold of the soft
start circuit is crossed, the same Softstart sequence
mentioned previously is repeated. This sequence is
repeated until the over condition is removed.
Mosfet gate drive can be provided by an external 12V
supply that is connected from BST to GND. The
actual gate to source voltage of the upper Mosfet will
approximately equal 7V (12V-VCC). If the external
12V supply is not available, a classical boot strap
technique can be implemented from the VCC supply.
A boot strap capacitor is connected from BST to
Phase while VCC is connected through a diode
(Schottky or other fast low VF diode) to the BST. This
will provide a gate to source voltage approximately to
VCC-Vdiode drop.
Lower Gate
Lower Gate
Upper Gate
PhaseNode
Lower Gate
PhaseNode
Vtt Shorted
Shoot through control circuitry provides a 100ns dead
time to ensure both upper and lower MOSFET will not
turn on simultaneously and cause a shoot through
condition.
Upper Gate
Lower Gate
GATE DRIVERS
The Low side gate driver is supplied from VCC and
provide a peak source/sink current of and 500mA.
The high side gate drive is also capable of sourcing
and sinking peak currents of 500mA. The high side
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