MP3310N—50V, 1.3A, STEP-UP WHITE LED DRIVER WITH TRUE PWM DIMMING
OPERATION
The MP3310N employs a constant frequency,
peak current mode step-up converter and internal
regulated current source to regulate the array of
white LEDs. The operation of the MP3310N can
be understood by referring to the block diagram
of Figure 1.
error amplifier (VCOMP) the power FET is turned
off.
The COMP voltage at the output of the internal
error amplifier is an amplified signal of the
difference between the 500mV reference voltage
and the feedback voltage. The converter
automatically provides enough bus voltage to
power the LED array.
Internal 5V Regulator
The MP3310N includes an internal linear
regulator (VCC). When VIN is greater than 5.5V,
this regulator offers a 5V power supply for the
internal MOSFET switch gate driver and the
internal control circuitry. The VCC voltage drops
to 0V when the chip shuts down. In the
application of VIN smaller than 5.5V, tie VCC
and VIN together. The MP3310N features Under
Voltage Lockout. The chip is disabled until VCC
exceeds the UVLO threshold. And the hysteresis
of UVLO is approximately 450mV.
If the feedback voltage drops below the 500mV
reference, the output of the error amplifier
increases. It results in more current flowing
through the power FET, thus increasing the
power delivered to the output. In this way it forms
a close loop to make the LED current in
regulation.
At light-load or VOUT near to VIN operation, the
converter runs into the pulse-skipping mode, the
FET is turned on for a minimum on-time, and
then the converter discharges the power to the
output in the remnant period. The FET will keep
off until the output voltage needs to be boosted
again.
System Startup
When the MP3310N is enabled and VCC
exceeds the UVLO threshold, the capacitor on
COMP pin is charged. Once the COMP level
reaches to about 750mV, the switching begins
and the MP3310N starts boosting the step-up
converter.
Dimming Control
The MP3310N incorporates both Enable and
PWM dimming onto a single control pin. The part
features true PWM dimming which results in
PWM chopping of the current in the LEDs to
provide flexible LED brightness control.
Step-up Converter
The converter operation frequency is adjustable
by FSET setting resistor, which is helpful for
optimizing the external components sizes and
improving the efficiency.
Open Load Protection
The open load protection is achieved through the
over voltage protection. If LED array is open, the
LED pin is pulled to ground and the IC keeps
charging the output voltage until it reach OVP
threshold. Then MP3310 turns off the internal
switch and recovers when VOVP falls to hysteresis.
At the beginning of each cycle, the power FET is
turned on with the internal clock. To prevent sub-
harmonic oscillations at duty cycles greater than
50 percent, a stabilizing ramp is added to the
output of the current sense amplifier and the
result is fed into the PWM comparator. When this
result voltage reaches the output voltage of the
MP3310N Rev.1.0
12/2/2014
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2014 MPS. All Rights Reserved.
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