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LT3972

3972f

BD (Pin 1): This pin connects to the anode of the boost

Schottky diode. BD also supplies current to the internal

regulator.

BOOST (Pin 2): This pin is used to provide a drive

voltage, higher than the input voltage, to the internal bipolar

NPN power switch.

SW (Pin 3): The SW pin is the output of the internal power

switch. Connect this pin to the inductor, catch diode and

boost capacitor.

VIN (Pin 4): The VIN pin supplies current to the LT3972’s

internal regulator and to the internal power switch. This

pin must be locally bypassed.

RUN/SS (Pin 5): The RUN/SS pin is used to put the

LT3972 in shutdown mode. Tie to ground to shut down

the LT3972. Tie to 2.5V or more for normal operation. If

the shutdown feature is not used, tie this pin to the VIN

pin. RUN/SS also provides a soft-start function; see the

Applications Information section.

SYNC (Pin 6): This is the external clock synchronization

input. Ground this pin for low ripple Burst Mode operation at

low output loads. Tie to a clock source for synchronization.

Clock edges should have rise and fall times faster than 1μs.

Tie Pin to GND if not used. See Synchronization section

in Applications Information.

PG (Pin 7): The PG pin is the open collector output of an

internal comparator. PG remains low until the FB pin is

within 9% of the ﬁnal regulation voltage. PG output is valid

when VIN is above 3.6V and RUN/SS is high.

FB (Pin 8): The LT3972 regulates the FB pin to 0.790V.

Connect the feedback resistor divider tap to this pin.

VC (Pin 9): The VC pin is the output of the internal error

ampliﬁer. The voltage on this pin controls the peak switch

current. Tie an RC network from this pin to ground to

compensate the control loop.

RT (Pin 10): Oscillator Resistor Input. Connecting a resistor

to ground from this pin sets the switching frequency.

Exposed Pad (Pin 11): Ground. The Exposed Pad must

be soldered to PCB.

–

OSCILLATOR

200kHzTO2.4MHz

BurstMode

DETECT

VC CLAMP

SOFT-START

SLOPE COMP

VIN

RUN/SS

BOOST

SWITCH

LATCH

VOUT

DISABLE

GND

ERROR AMP

0.73V

3680 BD

INTERNAL 0.79V REF

SYNC

BLOCK DIAGRAM

PIN FUNCTIONS

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