MP3367

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

MP3367 Rev. 1.0

www.MonolithicPower.com

15

6/17/2019

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does not change based on the input PWM

dimming

frequency.

The

output

dimming

frequency is selected with the mix dimming

output frequency selection bit through the I2C.

This function eliminates audible noise and

improves the dimming performance in small

dimming ratio.

<25%, PDIM

Duty = 4 * DPWMI, ILED = ¼ ISET

PWM

ILED

25%

>25%, ADIM

ILED = DPWM * ISET

ISET

Figure 2: Mix Dimming with 25% Transfer Point

Direct PWM Dimming

Connect a resistor to set MIX/AD to a middle

level (0.5V to 0.8V), or float MIX/AD and set the

internal mode-select register MODE1:0 = 01

through the I2C.

When a PWM signal is applied to DIM, the

amplitude of the LED current remains at the LED

full-scale, and the LED current is chopped by the

input PWM signal. The LED current duty follows

the PWM input duty, and the LED current

frequency is the same as the PWM input.

Analog Dimming Mode

Connect a resistor to set MIX/AD to a high level

(1V to 1.3V), or float MIX/AD and set the internal

mode-select register MODE = 10 through the I2C.

The PWM input signal is calculated by an

internal counter. The amplitude of the LED

current is equal to ISET * DDIM, where ISET is the

full-scale LED current and DDIM is the duty of the

input PWM signal. For better analog dimming

performance, a 100Hz to 20kHz PWM signal is

recommended.

To ensure good performance with a small

dimming ratio, the minimum LEDX voltage shifts

up to 2V when the dimming duty is below 10%.

Analog dimming supports a 200:1 dimming ratio.

Deep Dimming Ratio for PWM Dimming

When the output dimming on-time is less than

7

μs, the output voltage is regulated to 0.93 of the

OVP voltage (see Figure 3).

PWM

Vo

VSW

0.93*VOVP

<7µs

Figure 3: Deep Dimming Ratio for PWM Dimming

Unused LED Channel Setting

If the LEDX pin of an unused channel is

connected to GND, the MP3367 automatically

detects the unused LED string and removes it

from

the

control

loop

during

start-up.

If

employing five strings, connect LED6 to GND. If

using four strings, connect LED5 and LED6 to

GND, and so on.

The MP3367 can also disable the unused string

by the internal register (CH2:0 bit).

CH2:0 = 000: All six channels are in use

CH2:0 = 001: LED1-5 in use

CH2:0 = 010: LED1-4 in use

CH2:0 = 011: LED1-3 in use

CH2:0 = 100: LED1-2 in use

CH2:0 = 101: LED1 in use

Phase Shift Function

To reduce inrush current and eliminate audible

noise during PWM dimming, the MP3367

employs a phase shift function. Two methods

can be used to enable the phase shift function:

The first option is to connect SCL/PSE and

SDA/PSE together to 0.75V ~ 1V.

The second is to set the internal register PSE bit

to 1 through the I2C.

The LED channels

’ current source is phase-

shifted when the IC employs PWM dimming. The

shifted phase depends on which LED channels

are in use, determined using Equation (2):

 



360

Phase( )

( )

n

(2)

Where n is the LED channel in use. If all six

channels are in use, the shifted phase is 60°.