D =

LM2734

BOOST

SW

GND

L

D1

D2

D3

R3

C4

VBOOST

V

IN

C

IN

V

OUT

C

OUT

LM2734Z

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SNVS334D – JANUARY 2005 – REVISED JUNE 2008

ENABLE PIN / SHUTDOWN MODE

The LM2734Z has a shutdown mode that is controlled by the enable pin (EN). When a logic low voltage is

applied to EN, the part is in shutdown mode and its quiescent current drops to typically 30nA. Switch leakage

SOFT-START

reference voltage ramps from 0V to its nominal value of 0.8V in approximately 200µs. This forces the regulator

output to ramp up in a more linear and controlled fashion, which helps reduce inrush current.

OUTPUT OVERVOLTAGE PROTECTION

The overvoltage comparator compares the FB pin voltage to a voltage that is 10% higher than the internal

reference Vref. Once the FB pin voltage goes 10% above the internal reference, the internal NMOS control

switch is turned off, which allows the output voltage to decrease toward regulation.

UNDERVOLTAGE LOCKOUT

Undervoltage lockout (UVLO) prevents the LM2734Z from operating until the input voltage exceeds 2.74V(typ).

CURRENT LIMIT

The LM2734Z uses cycle-by-cycle current limiting to protect the output switch. During each switching cycle, a

current limit comparator detects if the output switch current exceeds 1.7A (typ), and turns off the switch until the

next switching cycle begins.

THERMAL SHUTDOWN

Thermal shutdown limits total power dissipation by turning off the output switch when the IC junction temperature

exceeds 165°C. After thermal shutdown occurs, the output switch doesn’t turn on until the junction temperature

drops to approximately 150°C.

Design Guide

INDUCTOR SELECTION

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Copyright © 2005–2008, Texas Instruments Incorporated

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