LP3367 datasheet(8/10 Pages) POWER

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LP3367-02

Feb.-2011

Email: marketing@lowpowersemi.com

www.lowpowersemi.com

Page 8 of 10

Preliminary Datasheet

LP3367

Function Description

The LP3367 Buck/Boost charge pump is designed

for converting a Li-Ion battery voltage of 2.7V to 4.2V

to drive a white LED used in digital still camera Flash

and Torch applications. The LP3367 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.

The LP3367 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 LP3367 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 LP3367 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 LP3367 automatically switches to the 2x

mode. The LP3367 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 LP3367, 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 (FLASH=GND), the FLASH pin

is set to logic low and the LP3367 FB pin regulates to

50mV output:

VFB=50mV (Touch mode)

In the FLASH mode, (FALSH=VIN), the FB

regulation voltage is set by the external resistor

(RSET) connected between the RSET pin and

SGND 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

Flash Timeout Protection

Due to the high currents typically available in Flash

mode, it is necessary to protect the white LED from

damage if left on too long. The LP3367 has a timeout

in Flash mode of approximately 1.6 seconds after

which it will shut down operation. Operation will not

begin again in Flash mode until the EN pin or FLASH

pin have been set Low and then High again.

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.

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