MP3362

– SINGLE-STRING, 3V MINIMUM Vin, 36V BOOST LED DRIVER

MP3362 Rev. 1.1

www.MonolithicPower.com

11

2/22/2023

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OPERATION

The MP3362 drives the internal MOSFET with

current mode architecture to regulate the LED

current, which is measured through an external

current-sense resistor.

The MP3362 employs a special circuit to regulate

the internal power supply, which covers a wide

input voltage range. The switching frequency can

be configured. The device integrates under-

voltage lockout (UVLO), over-voltage protection

(OVP), over-current protection (OCP), short LED

protection, short FB to GND protection, short

inductor/diode protection, and thermal protection.

Step-Up Converter

The MP3362 uses peak current control mode to

regulate the output energy. At the beginning of

each switching cycle, the internal clock turns on

the internal N-channel MOSFET (in normal

operation, the minimum turn-on time is about

50ns). A stabilizing ramp is added to the output of

the

current-sense

amplifier

to

prevent

subharmonic

oscillations

for

duty

cycles

exceeding 50%. This result is fed into the PWM

comparator. If the summed voltage reaches the

output voltage of the error amplifier, the internal

MOSFET turns off (for improved stability, the turn-

off time should exceeds 100ns).

The output voltage of the internal error amplifier is

an amplified signal of the difference between the

reference voltage and the FB voltage.

If the feedback voltage drops below the reference

voltage, the output of the error amplifier increases.

This results in more current flowing through the

MOSFET, which increases the power delivered to

the output. This forms a closed loop that regulates

the output voltage.

If VOUT is almost equal to VIN under light-load

conditions, the converter runs in pulse-skip mode.

The MOSFET turns on for a minimum on time, and

then the converter discharges the power to the

output for the remaining period. The internal

MOSFET remains off until the output voltage

requires another boost.

Soft Start

The MP3362 implements soft start by limiting the

current capability of the internal error amplifier

during start-up. The COMP voltage jumps to its

clamp voltage at the beginning of start-up. The

source/sink current of the internal error amplifier is

limited to about 10µA until the FB voltage reaches

80% of the internal reference voltage during start-

up. The maximum soft-start time is limited to 10ms

to prevent the IC from always being in soft start

during deep analog dimming.

VEN/DIM

VCOMP

ILED

0.8 x

ILED

VIN

Figure 2: Soft Start

Enable (EN) and Dimming (DIM)

The EN/DIM pin can be used for different functions

when different signals are applied on this pin.

These functions are described below:

1. Enable/disable: If the EN/DIM pin is pulled

high, the IC is enabled; if the EN/DIM pin is

pulled low for 20ms, the IC is disabled.

2. PWM dimming (fPWM < 2kHz): If the PWM

signal has a frequency below 2kHz, the IC

operates in PWM dimming mode. If the PWM

signal is low in PWM dimming mode, the IC

stops switching, and the output voltage and

output current drop. If the PWM signal is high,

the IC starts switching, and the output voltage

and output current begin to rise. This condition

prohibits soft start.

3. Analog dimming (fPWM > 5kHz): If the PWM

signal has a frequency exceeding 5kHz, the IC

operates in analog dimming mode. The LED

current can be changed by changing the PWM

duty cycle.