MP3383

– 4-STRING, MAX 80V VOUT, STEP-UP WLED CONTROLLER

MP3383 Rev. 1.0

MonolithicPower.com

14

5/2/2022

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

© 2022 MPS. All Rights Reserved.

OPERATION

The

MP3383

is

a

configurable

constant-

frequency, peak current control mode, step-up

converter with 4-channel regulated current

sources to drive an array of up to four white LED

strings.

Internal 12V Regulator

The MP3383 includes an internal linear regulator

(VCC). When the input voltage (VIN) exceeds

13V, VCC outputs a 12V power supply to the

external MOSFET gate driver and the internal

control circuitry. The VCC voltage (VCC) drops to

0V when the chip shuts down. The MP3383

features under-voltage lockout (UVLO). The chip

is

disabled until

VCC exceeds the UVLO

threshold.

The

UVLO

hysteresis

is

approximately 500mV.

System Start-Up

When enabled, the MP3383 checks the topology

connection first by monitoring the over-voltage

protection (OVP) pin. This determines whether a

Schottky diode is connected or the boost output

is shorted to GND. An OVP voltage (VOVP)

exceeding 50mV allows the chip to switch

normally. Otherwise, switching is disabled. The

MP3383 also checks other safety limits after

passing the OVP test, including UVLO, over-

temperature protection (OTP), and over-current

protection (OCP). If all protection tests pass, the

chip then begins boosting the step-up converter

with an internal soft start (SS).

To prevent a large inrush current, the enable

(EN) signal should occur after the establishment

of VIN and the pulse-width modulation (PWM)

dimming signal during the start-up sequence.

Step-Up Converter

At the beginning of each switching cycle, the

internal clock turns on the external MOSFET.

During normal operation, the minimum turn-on

time of the external MOSFET is around 150ns.

Adding a stabilizing ramp to the current-sense

amplifier

’s

output

prevents

subharmonic

oscillations for duty cycles greater than 50%,

which is then fed into the PWM comparator.

When the summed voltage reaches the error

amplifier

(EA)’s output voltage (VCOMP), the

external MOSFET turns off.

VCOMP is an amplified signal of the difference

between the reference voltage (VREF) and the

feedback

voltage

(VFB).

The

converter

automatically chooses the lowest active LEDx

pin voltage (VLEDx) to provide a sufficient bus

voltage to power all LED strings.

If VFB drops below VREF, the EA’s output voltage

(VCOMP) increases. This results in more current

flowing through the MOSFET, increasing the

power delivered to the output and forming a

closed loop that regulates the output voltage

(VOUT).

Under light-load operation, especially if VOUT ≈

VIN, the converter runs in pulse-skipping mode.

In this mode, the MOSFET turns on for a

minimum on time and then the converter

discharges the power to the load for the

remaining

period.

The

external

MOSFET

remains off until VOUT must be boosted again.

Dimming Control

The MP3383 provides two dimming methods:

PWM dimming and analog dimming.

For PWM dimming, apply a PWM signal to the

PWM pin. The LED current (ILED) is chopped by

this PWM signal, and the average ILED is equal to

ISET x DDIM, where DDIM is the PWM dimming

signal’s duty cycle, and ISET is the full-scale ILED

set by the ISET resistance (RISET).

For analog dimming, apply a PWM signal to the

ADIM pin. An internal RC filter (10M

Ω resistor

and 100pF capacitor) is integrated to ADIM. This

PWM signal is filtered to the DC voltage by the

internal RC filter. The ILED amplitude is equal to

ISET x DDIM, where DDIM is the PWM dimming

signal’s duty cycle, and ISET is the full-scale ILED

set by RISET. A 20kHz or greater PWM signal is

recommended for improved filtering.

Operating Switching Frequency (fSW)

The MP3383

’s switching frequency (fSW) is set

through an external resistor on the OSC pin. This

helps optimize both the size of the external

components and system efficiency

.