MP1519L – 1X, 1.5X, 2X CHARGE PUMP 3 WHITE LED DRIVER

MP1519L Rev. 1.3

www.MonolithicPower.com

6

7/27/2006

MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.

© 2006 MPS. All Rights Reserved.

TM

APPLICATION INFORMATION

COMPONENT SELECTION

Startup

When power is applied to the BATT, driving EN

high will enable the MP1519L. The MP1519L

begins by checking for open LEDs and

determining the optimum charge pump mode.

The lowest charge pump mode that allows the

programmed LED current in all LEDs is set.

This will occur during initial turn-on or during

analog mode and burst mode dimming.

Shutdown

Driving EN low for more than 30µs will disable

the MP1519L. For safety the MP1519L runs a

small supervisory circuit in standby to protect

the charge pump output LEDC. The circuit

shuts down when the charge pump output

returns to zero volts (this can take a few

seconds). The MP1519L is in true shutdown

mode when LEDC is zero and the 30µs time

interval has passed. The supply current should

be less than 1µA.

Setting the LED Current

The LED regulation current is set through the

resistor R1 (refer to the typical application circuit

on page 1). The voltage across R1 is fixed at

1.25V, and the current through that resistor sets

the current through the LEDs.

25

20

15

10

5

0

0

5

10

15

20

Choose R1 for the desired LED current

according to the equation:

LED

I

31.25

R1

=

values for R1 are greater than 1.2kΩ.

Soft-Start

During startup and mode switching, an internal

soft-start prevents excessive input current,

preventing excessive loading of the battery or

input power source.

Burst Mode Dimming

To dim the part using burst mode, drive EN with

a PWM signal. Each time EN is driven high, the

MP1519L goes through the initial startup

routine and checks for open LEDs, and the

charge pump step-up mode is reset.

When

EN

goes

low,

the

LED

current

immediately goes to zero. After EN is held low

for 30µs or longer, and LEDC falls below GND,

the MP1519L operating current drops below

1µA to improve battery life. Maintain the

frequency of the PWM signal between 50Hz

and 50KHz. Going above 50KHz the accuracy

of the PWM signal will be degraded due to the

startup time, and below 50Hz, the LED flicker

will be evident to the eye.

Ideally,

the

LED

current

increases

proportionally with the duty cycle of the PWM

signal and is independent of the dimming

frequency.

Analog Mode Dimming

Analog dimming can be accomplished with the

circuit in Figure 3. The circuit provides 1mA to

minimum LED current the MP1519L can

regulate is approximately 1mA.