3724EFE View Datasheet(PDF) - Linear Technology

Part Name

Description

Manufacturer

3724EFE

High Voltage, Current Mode Switching Regulator Controller

Linear Technology 

LT3724

PIN FUNCTIONS

VCC (Pin 12): The VCC pin is the internal bias supply

decoupling node. Use a low ESR 1µF ceramic capacitor

to decouple this node to PGND. Most internal IC func-

tions are powered from this bias supply. An external

diode connected from VCC to the BOOST pin charges the

bootstrapped capacitor during the off-time of the main

power switch. Back driving the VCC pin from an external

DC voltage source, such as the VOUT output of the buck

regulator supply, increases overall efficiency and reduces

power dissipation in the IC. In shutdown mode this pin

sinks 20µA until the pin voltage is discharged to 0V.

NC (Pin 13): No Connection.

SW (Pin 14): In step-down applications the SW pin is

connected to the cathode of an external clamping Schottky

diode, the source of the power MOSFET and the induc-

tor. The SW node voltage swing is from VIN during the

on-time of the power MOSFET, to a Schottky voltage drop

below ground during the off-time of the power MOSFET.

In start-up and in operating modes where there is insuf-

ficient inductor current to freewheel the Schottky diode, an

internal switch is turned on to pull the SW pin to ground

so that the BOOST pin capacitor can be charged. Give

careful consideration in choosing the Schottky diode to

limit the negative voltage swing on the SW pin.

TG (Pin 15): The TG pin is the bootstrapped gate drive

for the top N-Channel MOSFET. Since very fast high cur-

rents are driven from this pin, connect it to the gate of

the power MOSFET with a short and wide, typically 0.02”

width, PCB trace to minimize inductance.

BOOST (Pin 16): The BOOST pin is the supply for the

bootstrapped gate drive and is externally connected to a

low ESR ceramic boost capacitor referenced to SW pin.

The recommended value of the BOOST capacitor, CBOOST,

is 50 times greater than the total input capacitance of the

topside MOSFET. In most applications 0.1µF is adequate.

The maximum voltage that this pin sees is VIN + VCC,

ground referred.

Exposed Pad (SGND) (Pin 17): The exposed leadframe is

internally connected to the SGND pin. Solder the exposed

pad to the PCB ground for electrical contact and optimal

thermal performance.

3724fd

7

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