MP3363

– SINGLE-STRING, 1.8V MINIMUM VIN, 36 VOUT BOOST LED DRIVER

MP3363 Rev. 1.0

MonolithicPower.com

9

9/28/2021

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OPERATION

The MP3363 drives the internal MOSFET with

current mode architecture to regulate the LED

current (ILED), which is measured through an

external current-sense (CS) resistor.

The MP3363 employs a special circuit to

regulate the internal power supply, which

covers a wide input voltage (VIN) range (1.8V to

36V). The switching frequency (fSW) 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, and

thermal shutdown (TSD).

Step-Up Converter

The MP3363 uses peak current control mode to

regulate the output power. 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 CS

amplifier

output

to

prevent

subharmonic

oscillations for duty cycles exceeding 50%. This

result is fed into the pulse-width modulation

(PWM) comparator. If the summed voltage

reaches the output voltage of the error amplifier

(EA), the internal MOSFET turns off.

The output voltage of the internal EA is an

amplified signal of the difference between the

reference voltage (VREF) and the FB voltage

(VFB).

If VFB drops below VREF, the EA’s output

increases. This results in more current flowing

through the MOSFET, which increases power

delivered to the output. This forms a closed

loop that regulates the output voltage (VOUT).

If VOUT is almost equal to VIN under light-load

conditions, the converter runs in pulse-skipping

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 VOUT

requires another boost.

Soft Start

The MP3363 implements soft start (SS) by

limiting the current capability of the internal EA

during start-up. The COMP voltage (VCOMP)

jumps to its clamp voltage at the beginning of

start-up. The source/sink current of the internal

EA is limited to about 10

μA until VFB reaches

80% of the internal VREF during start-up. The

maximum soft-start time is limited to 10ms. This

prevents the IC from always being in soft start

during deep analog dimming.

VEN/DIM

VCOMP

ILED

80% of ILED

VIN

Figure 2: Soft Start Process

Enable (EN) and Dimming (DIM)

The EN/DIM pin can be used for different

functions when different signals are applied on

the pin. These functions are described in

greater detail as 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

current (IOUT) and VOUT drop. If the PWM

signal is high, the IC starts switching, and

IOUT and VOUT begin to rise. This condition

prohibits soft start.

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

signal has a frequency above 5kHz, the IC

operates in analog dimming mode. The LED

current (ILED) can be changed by changing

the PWM duty cycle.

ILED can be calculated with Equation (1):