MP1519 – 1X, 1.5X, 2X CHARGE PUMP 4 WHITE LED DRIVER

MP1519 Rev. 1.9

www.MonolithicPower.com

6

7/27/2006

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© 2006 MPS. All Rights Reserved.

TM

APPLICATION INFORMATION

COMPONENT SELECTION

Startup

When power is applied to the BATT, driving EN

high will enable the MP1519. The MP1519 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 MP1519. For safety the MP1519 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 MP1519 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

MP1519 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 MP1519

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

LED current the MP1519 can regulate is

approximately 1mA.

LEDC

Do not drive or force LEDC as it may be shorted

to ground or may be pumped down by the

controller in the MP1519 at any time. Excessive

capacitance on the LEDC node can cause the

internal controller to time out before the charge

pump can be ready. Missing the timeouts will

cause excessive pumping and a loss of efficiency.

The MP1519 requires C1 and C2 be of the same

value and type.