LP3367 datasheet(9/10 Pages) POWER

9 / 10 page

LP3367-02

Feb.-2011

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Page 9 of 10

Preliminary Datasheet

LP3367

Over-Current Protection

The Over-Current Protection circuitry monitors the

average current out of the FB pin. If the average

current exceeds the two times set current, then the

over current protection circuitry shuts off the output

switches to protect the chip.

Brightness Control Using PWM

Dimming control can be achieved by applying a

PWM control signal to the EN pin. The brightness of

the white LEDs is controlled by increasing and

decreasing the duty cycle of the PWM signal. While

the operating frequency range of the PWM control is

from 60Hz to 700Hz, the recommended maximum

brightness frequency range of the PWM signal is

from 60Hz to 200Hz. A repetition rate of at least

60Hz is required to prevent flicker.

Application Information

The LP3367 charge pump circuit requires 3

capacitors: 1μF input, 1μF output and 1μF fly

capacitors are typically recommended. For the input

capacitor, a value of 10μF will help reduce input

voltage ripple for applications sensitive to ripple on

the battery voltage. All the capacitors should be

surface mount for low lead inductance necessary at

the 2MHz switching frequency of the LP3367 and to

obtain low ESR, which improves bypassing on the

input and output and improves output voltage drive

by reducing output resistance. The input and output

capacitors should be located as close to the VIN and

VOUT pins as possible to obtain best bypassing, and

the returns should be connected directly to the

PGND pin or to the thermal pad ground located

under the LP3367. The fly capacitor should be

located as close to the C1 and C2 pins as possible.

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