LM2734

BOOST

SW

GND

L

D1

D2

D3

R3

C4

VBOOST

V

IN

C

IN

V

OUT

C

OUT

LM2734Z, LM2734Z-Q1

SNVS334F – JANUARY 2005 – REVISED JANUARY 2016

www.ti.com

Feature Description (continued)

Resistor R3 must be chosen to provide enough RMS current to the Zener diode (D3) and to the BOOST pin. A

gate current of the NMOS control switch and varies typically according to Equation 8.

where

•

D is the duty cycle

•

•

•

•

(8)

NOTE

(9)

R3 is then given by Equation 10.

(10)

(11)

R3 = (10 V - 5 V) / (1.25 × 4.3 mA + 1 mA) = 787

Ω

(12)

7.3.3 Soft-Start

of the error amplifier ramps from 0 V to its nominal value of 0.8 V in approximately 200 µs. This forces the

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

7.3.4 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.

10

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