LTC3863 Datasheet, PDF (12/36 Pages) Linear Technology – 60V Low IQ Inverting DC/DC Controller Wide Operating VIN Range: 3.5V to 60V

LTC3863
OPERATION
The oscillator’s default frequency is based on the operating
frequency set by the FREQ pin. If the oscillator’s default
frequency is near the external clock frequency, only slight
adjustments are needed for the PLL to synchronize the
external P-channel MOSFET’s turn-on edge to the rising
edge of the external clock. This allows the PLL to lock
rapidly without deviating far from the desired frequency.
The PLL is guaranteed from 75kHz to 750kHz. The clock
input levels should be greater than 2V for HI and less
than 0.5V for LO.
Fault Protection
When the V_FB voltage is above +10% of the regulated
voltage of 0.8V, this is considered as an overvoltage con-
dition and the external P-MOSFET is immediately turned
off and prevented from ever turning on until V_FB returns
below +7.5%.
In the event of an output short circuit or overcurrent con-
dition that causes the output voltage to drop significantly
while in current limit, the LTC3863 operating frequency
will fold back. Anytime the output feedback V_FB voltage is
less than 50% of the 0.8V internal reference (i.e., 0.4V),
frequency foldback is active. The frequency will continue
to drop as V_FB drops until reaching a minimum foldback
frequency of about 18% of the setpoint frequency. Fre-
quency foldback is designed, in combination with peak
current limit, to limit current in start-up and short-circuit
conditions. Setting the foldback frequency as a percentage
of operating frequency assures that start-up characteristics
scale appropriately with operating frequency.
3863f
12
For more information www.linear.com/3863