TM
MP1519L – 1X, 1.5X, 2X CHARGE PUMP 3 WHITE LED DRIVER
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.
Figure 2 shows LED Current (I
LED
) vs. R1 with
V
BATT
= 3.6V.
25
LED CURRENT (mA)
Choose R1 for the desired LED current
according to the equation:
R1=
31.25
I
LED
Where R1 is in kΩ, and I
LED
is in mA. Suitable
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
15mA dimming with V
DC
= 0 to 3V. The
minimum LED current the MP1519L can
regulate is approximately 1mA.
20
15
10
5
0
0
5
10
15
20
Figure 2—I
LED
vs. R1
MP1519L Rev. 1.3
10/8/2007
www.MonolithicPower.com
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6
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