MP3214 – 500mA LED CAMERA FLASH CHARGE PUMP

MP3214 Rev. 1.01

www.MonolithicPower.com

8

6/24/2011

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

© 2011 MPS. All Rights Reserved.

OPERATION

Using the Enable Pin to PWM the LED

Current

The Enable (En) pin can enable (logic 1) or

disable (logic 0) the part. When disabled, the

part enters a low current sleep mode.

There is an internal one shot on the enable pin.

The enable pin must go low for more than

30mS in order to completely disable the part

and enter the low current shutdown mode.

Although

the

part

internally

does

not

immediately shut off, the output drive to the

LED does immediately turn off.

A low frequency PWM on the enable pin (50Hz

to 2kHz) can be used to change the LED

brightness. For example, if a 20% duty cycle

PWM signal is applied to the enable pin, the

average output current is 20% the full current.

Setting the Output Current

The output current follows the equation:

OUT

SET

3570

I

R

=

SET

OUT

3570

R

I

=

For example:

7140Ω

500mA

8925Ω

400mA

11900Ω

300mA

17850Ω

200mA

35700Ω

100mA

Charge Pump Operation

Normal battery operation will supply a voltage

that is initially high (roughly 4.2volts when fully

charge) falling to a mid voltage for much of it’s

life ( roughly 3 to 3.6 volts) and finally dropping

to a low voltage (roughly 2.7 to 3.0 volts) when

fully discharged. At the high end of the battery

voltage, the LED can be driven directly from the

battery to ground. As the battery discharges,

the voltage must be boosted to allow enough

forward voltage to turn on the LED. On the

MP3214, the boost voltage pushes the charge

pump output (CP) below ground to gain the

required headroom.

The charge pump gain can be changed on the

fly to optimize the charge pump voltage for

maximum efficiency.

The gain can be

configured to be 1, 1.5 or 2. The charge pump

gain control is accomplished automatically by

an internal feedback network.

Time Out Enable

The TOE function acts to extend the device

operation, for a period of time, after the enabled

pin goes low. With TOE=1 the time out is

enabled. When the enable pin goes high, the

part turns on as in normal operation. When the

enable pin goes low, the part and the output,

remain on for an extra 1.55 seconds.

When TOE=0, the enabled pin functions directly

bases on the logic level of the input. The part

turns on when enable is high, and off when

enable is low.