LT3980 datasheet(7/24 Pages) LINER

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LT3980

3980fa

For more information www.linear.com/LT3980

SYNC (Pin 1/Pin 1): This is the external clock synchro-

nization input. Ground this pin for low ripple Burst Mode

operation at low output loads. Tie to a voltage above 0.8V

to select pulse-skipping mode. 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 the

Synchronization section in Applications Information.

NC (Pins 2, 13/Pins 3, 5, 13, 16): No Connect. These

pins are not connected to internal circuitry.

PG (Pin 3/Pin 2): 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(Pin4/Pin4):TheLT3980regulatestheFBpinto0.790V.

Connect the feedback resistor divider tap to this pin.

VC (Pin 5/Pin 6): 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 6/Pin 7): Oscillator Resistor Input. Connecting

a resistor to ground from this pin sets the switching

frequency.

GND (Pin 7, 15/Pin 8, 17): Ground. The exposed pads

must be soldered to the PCB.

RUN/SS (Pin 8/Pin 9): The RUN/SS pin is used to put the

LT3980 in shutdown mode. Tie to ground to shut down

the LT3980. 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.

BD (Pin 9/Pin 10): This pin connects to the anode of the

boost Schottky diode. BD also supplies current to the

internal regulator.

BOOST (Pin 10/Pin 11): This pin is used to provide a drive

voltage,higherthantheinputvoltage,totheinternalbipolar

NPN power switch.

SW (Pin 11/Pin 12): The SW pin is the output of the

internal power switch. Connect this pin to the inductor,

catch diode and boost capacitor.

VIN (Pin 12/Pin 14): The VIN pin supplies current to the

LT3980’sinternalregulatorandtotheinternalpowerswitch.

This pin must be locally bypassed.

DA (Pin 14/Pin 15): This pin measures catch diode current

and pauses the oscillator during overcurrent conditions.

–

OSCILLATOR

100kHzTO2.4MHz

BurstMode

DETECT

VC CLAMP

SOFT-START

SLOPE COMP

VIN

RUN/SS

BOOST

SWITCH

LATCH

VOUT

DISABLE

GND

ERROR AMP

0.725V

3680 BD

INTERNAL 0.79V REF

SYNC

block DiaGram

pin FuncTions (DFN, MSOP)

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