TB62731FUG 데이터 시트보기 (PDF) - Marktech Optoelectronics

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TB62731FUG

Step-up DC-DC Converter for White LED Driver

Marktech Optoelectronics 

TB62731FUG

VCC

IL, ILpeak

A

OSC

350 kHz

SHDN

VIN C1

STB

SQ

R

Buffer

REF

i (add)

A

i (sub)

NMOS

C2

Ic2

Io

K

R_sens

GND

Figure 1 Application Circuit

The basic TB62731FUG circuit uses a step-up DC-DC converter and burst control of the current pulse.

Basic Operation

The internal MOS transistor (NMOS) is turned on at fOSC = 350 kHz, charging energy to the inductor.

The inductance current IL increases from 0. When IL = ILpeak = 240 mA (typ.) or when 5/6 (83.3%) of fOSC (=

350 kHz) is reached, the transistor is turned off.

At that time, the coil maintains IL = ILpeak, the Schottky diode is turned on, and IL = Ic2 flows. Then, Ic2

decreases, reaching IL = 0.

The above operation repeats. When Ic2 is fully charged, the surplus current becomes Io, which flows to the

LED.

The graph below shows details of the basic pulse used for burst control.

IL, ILpeak

Maximum duty: 83.3% of fOSC

With low inductance

With high inductance

T = 1/fOSC, fOSC = 350 kHz (typ.)

Figure 2 Switching Waveform of Inductance

5

2004-09-14

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