MP3310—50V, 1.3A, STEP-UP WHITE LED DRIVER WITH TRUE PWM DIMMING

MP3310 Rev.1.0

www.MonolithicPower.com

7

7/5/2011

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© 2011 MPS. All Rights Reserved.

OPERATION

The MP3310 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 MP3310 can be

understood by referring to the block diagram of

Figure 1.

Internal 5V Regulator

The MP3310 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 MP3310 features Under Voltage Lockout.

The chip is disabled until VCC exceeds the

UVLO threshold. And the hysteresis of UVLO is

approximately 450mV.

System Startup

When the MP3310 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

MP3310 starts boosting the step-up converter.

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.

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

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.

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.

Dimming Control

The MP3310 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.

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 the MP3310 shuts down the

step-up converter.