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LT3505

3505fc

PIN FUNCTIONS

BOOST (Pin 1): The BOOST pin is used to provide a drive

voltage,higherthantheinputvoltage,totheinternalbipolar

NPN power switch.

SW (Pin 2): The SW pin is the output of the internal power

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

boost capacitor.

VIN (Pin 3): The VIN pin supplies current to the LT3505’s

internal regulator and to the internal power switch. This

pin must be locally bypassed.

SHDN (Pin 4): The SHDN pin is used to put the LT3505 in

shutdown mode. Tie to ground to shut down the LT3505.

Tie to 2.3V or more for normal operation. If the shutdown

feature is not used, tie this pin to the VIN pin. SHDN also

provides a soft-start function; see the Applications Infor-

mation section.

GND (Pin 5): Tie the GND pin to a local ground plane

below the LT3505 and the circuit components. Return the

feedback divider to this pin.

RT (Pin 6): The RT pin is used to program the switching

frequency of the LT3505 by connecting a resistor from

this pin to ground. The Applications Information section of

the data sheet includes a table to determine the resistance

value based on the desired switching frequency. Minimize

capacitance at this pin.

FB(Pin7):TheLT3505regulatesitsfeedbackpinto780mV.

Connect the feedback resistor divider tap to this pin. Set

the output voltage by selecting R1 according to:

OUT

0 78









–

A good value for R2 is 10.0k.

VC (Pin 8): The VC pin is used to compensate the LT3505

control loop by tying an external RC network from this

pin to ground.

Exposed Pad (Pin 9): The Exposed Pad must be soldered

to the PCB and electrically connected to ground. Use a

large ground plane and thermal vias to optimize thermal

performance.

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