MP3011 MPS, MP3011 Datasheet - Page 6

• Manufacturer Part Number: MP3011
• Description: High Efficiency Charge Pump 2 White LED Driver
• Manufacturer: MPS

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APPLICATION INFORMATION
COMPONENT SELECTION
Startup
When power is applied to the BATT pin, driving
EN high will enable the MP3011. The MP3011
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 MP3011. For safety the MP3011 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 MP3011 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
V
MP3011 Rev. 1.1
10/31/2005
BATT
= 3.6V.
50
40
30
20
10
0
Figure 2—I
TM
0
5
MP3011 – 1X, 1.5X, 2X AUTO-ADJUST CHARGE PUMP 2 WHITE LED DRIVER
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
LED
10
vs. R1
LED
15
) vs. R1 with
MP3011_F02
20
© 2005 MPS. All Rights Reserved.
www.MonolithicPower.com
Choose R1 for the desired LED current according
to the equation:
Where R1 is in kΩ and I
values for R1 are greater than 1.2kΩ.
Soft-Start
During startup and mode switching, an internal
soft-start
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
MP3011 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 MP3011
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 2mA to
30mA dimming with V
minimum LED current the MP3011 can regulate
is approximately 2mA.
LEDC
Do not drive or force LEDC as it may be shorted
to ground or may be pumped down by the
controller in the MP3011 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 MP3011 requires C1 and C2 be of the same
value and type.
prevents
R1=
excessive
62.5
I
DC
LED
LED
= 0V to 3V. The
is in mA. Suitable
input
current,
6