MP3367

– 6-CHANNEL BOOST WLED DRIVER WITH HIGH DIM RATIO AND I2C

MP3367 Rev. 1.0

www.MonolithicPower.com

14

6/17/2019

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© 2019 MPS. All Rights Reserved.

OPERATION

The MP3367 is a programmable, constant

frequency, peak current mode step-up converter

with up to six channels of regulated current

sources to drive the array of white LEDs.

Internal 5V Regulator

The MP3367 includes an internal linear regulator

(VCC). When VIN exceeds 6V, this regulator

outputs a 5V power supply to the internal

MOSFET switch gate driver and the internal

control circuitry. The VCC voltage drops to 0V

when the chip shuts down. The chip remains

disabled until VCC exceeds the UVLO threshold.

System Start-Up

When enabled, the MP3367 checks the topology

connection. The IC draws current from SD to

enable the input disconnect PMOS to be turned

on (if this PMOS is used). After a 500

μs delay,

the IC monitors OVP to see if the output is

shorted to GND. If the OVP voltage is less than

100mV, the IC disables and latches off. The

MP3367 then continues to check other safety

limits (e.g. LED open, over-voltage protection). If

all protection tests pass, the IC starts boosting

the step-up converter with an internal soft start.

The recommended power-on sequence is VIN 

EN  I2C (optional)  PWM dim signal.

Step-Up Converter

The MP3367 employs peak current mode control

to regulate the output energy. At the beginning

of each switching cycle, the internal clock turns

on the internal N-MOSFET. In normal operation,

the minimum turn-on time is about 100ns. A

stabilizing ramp added to the output of the

current-sense amplifier prevents sub-harmonic

oscillations for duty cycles greater than 50%.

This result is fed into the PWM comparator.

When the summed voltage reaches the output

voltage of the error amplifier, the internal

MOSFET turns off.

The output voltage of the internal error amplifier

is an amplified signal of the difference between

the reference voltage and the feedback voltage.

The converter automatically chooses the lowest

active LEDX pin voltage to provide a high

enough output voltage to power all the LED

arrays.

If the feedback

voltage drops

below

the

reference voltage, the output of the error

amplifier increases. More current then flows

through the MOSFET, increasing the power

delivered to the output. This forms a closed loop

that regulates the output voltage.

During light-load operation, especially in the

case of VOUT

≈ VIN, the converter runs in pulse-

skipping mode. In this mode, the MOSFET turns

on for a minimum on time, then the converter

discharges the power to the output for the

remaining

period.

The

external

MOSFET

remains off until the output voltage needs to be

boosted again.

Dimming Control

The MP3367 provides analog, PWM, and mix

dimming methods. Dimming mode can be set

with I2C or by connecting a different resistor at

MIX/AD. The voltage of MIX/AD is calculated

with Equation (1):

V_MIX/AD(mV) = 18(μA) × R_MIX/AD(kΩ)

(1)

Where V_MIX/AD is the voltage and R_MIX/AD is the

resistor at MIX/AD.

Mix Dimming Mode

There are two different ways the MP3367 works

in mixture dimming mode, with 25% or 12.5% as

its transfer point (selected through the internal

register).

The first option is to connect a resistor and set

MIX/AD to low (<0.3V).

The second is to float MIX/AD, and set the

internal mode-select register MODE1:0 = 00

through I2C.

A PWM dimming signal is applied to DIM. When

the dimming duty is greater than 25%, analog

dimming is adopted, and the LED current

amplitude follows the duty of PWM. When the

dimming duty is less than 25%, PWM dimming is

used (see Figure 2). The LED current amplitude

remains at 1/4 of the full-scale current, and the

output dimming duty is 4 times the duty of the

input PWM signal. There are two options for

output dimming frequency when using mix

dimming: 200Hz (default) or 23kHz (no audible

noise, but larger minimum dimming duty). This