LP3368 datasheet(6/8 Pages) POWER

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LP3368-02

May. -2014

Email: marketing@lowpowersemi.com

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Page 6 of 8

Preliminary Datasheet

LP3368

Function Description

The LP3368 is designed for converting a Li-Ion

battery voltage of 2.7V to 4.2V to drive two LEDs

used in digital still camera Flash and Smart Phone

applications. The LP3368 has two modes (Torch and

Flash). Torch mode can be used continuously at a

lower output current than Flash and is often used for

several seconds in a digital still camera “movie”

mode. Flash mode is usually used with a pulse of

about 200 to 300 milliseconds to generate a high

intensity Flash. Each channel can be operated

independently through EN1/2 or MODE1/2. The

LP3368 also has two modes of operation to control

the output current. The 1x mode and 2x mode.

Operation begins after the enable pin EN receives a

logic high, then LP3368 starts in the 1x mode, which

acts like a linear regulator to control the output

current by continuously monitoring the feedback pin

FB. In 1x mode, if the LP3368 auto detects a dropout

condition, which is when the FB pin is below the

regulation print for more than 32 cycles of the internal

clock, the LP3368 automatically switches to the 2x

mode. The LP3368 remains in the 2x mode until one

of four things happens: 1. The enable pin EN has

been toggled; 2. The Flash pin has changed from

high to low; 3. Vin is cycled or; 4. A thermal fault

occurs. The 2x mode is the charge pump mode

where the output can be pumped as high as two

times the input voltage, provided the output does not

exceed the maximum voltage for the LP3368, which

is internally limited to about 5.5V. In the 2x mode, as

in the 1x mode, the output current is regulated by the

voltage at the FB pin.

In the TORCH mode, the MODE1/2 pin is set to logic

low and the LP3368 FB pin regulates to 50mV

output:

VFB=50mV (Torch mode)

In the FLASH mode, (MODE=VIN), the FB regulation

voltage is set by the external resistor (RSET)

connected between the RSET pin and GND and the

equation:

VFB=1.26×11.2kΩ/RSET，(Flash mode)

Where 1.26V is the internal band gap reference

voltage and 11.2kΩ is an internal resistance used to

scale the RSET current. Typical values of RSET are

40kΩ to 180kΩ for a range of VFB=300mV to 75mV

in Flash mode.

The output current is then set in either Flash or Torch

mode by the equation:

IOUT= VFB/RSENSE

Over-Voltage Protection

The Over-Voltage Protection monitors the output

voltage. When the output voltage rises above 5.5V,

the Over-Voltage Protection shuts off all of the output

switches to prevent the output voltage from rising

further. When the output decreases below 5.5V, the

device resumes normal operation.

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.

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