MP3367

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

MP3367 Rev. 1.0

www.MonolithicPower.com

16

6/17/2019

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LED1 directly follows the input PWM signal, and

LED2 lags 60° behind (see Figure 4).

PWMI

ILED1

ILED2

ILED3

ILED6

t

60º

Figure 4: Phase Shift with Six Channels

Figure 5 shows the phase shift function with four

channels enabled. The shifted phase in this case

is 90°.

PWMI

ILED1

ILED2

ILED3

ILED4

t

90º

Figure 5: Phase Shift with Four Channels

In phase shift operation, the channels must be

disabled in descending order of channel number.

For example, if three strings are employed in

application, then channels 6, 5, and 4 are

disabled.

It is not recommended to tie two channels for one

string of LED with the phase shift function.

Frequency Spread Spectrum

The MP3367 uses switching frequency jitter to

spread the switching frequency spectrum. This

reduces the spectrum spike around the switching

frequency and its harmonic frequencies.

FSP can program the dithering range, and the

modulation frequency is fixed to 1/150 of

switching frequency. When FSP < 0.3V, the jitter

frequency is 1/20 of the central frequency. When

FSP = 0.4V to 1.4V, the jitter frequency is 1/32

of the central frequency. Float FSP to follow the

internal I2C setting.

The frequency jitter range selected by bit FSPR

selects the range. When FSPR = 0 (default), the

jitter frequency is 1/20 of the central frequency.

When FSPR = 1, the jitter frequency is 1/32 of

the central frequency.

The

modulation

frequency

is

selected

by

FSPMF1:0 bits. When FSPMF1:0 = 00, the

modulation frequency is 1/100 of the switching

frequency.

When

FSPMF1:0

=

01,

the

modulation frequency is 1/150 of the switching

frequency.

When

FSPMF1:0

=

10,

the

modulation frequency is 1/200 of the central

frequency. When FSPMF1:0 = 11, default, the

function is disabled.

Protection

The MP3367 includes open LED protection,

short LED protection, short LEDX to GND

protection, over-current protection, short VOUT

to GND protection, and thermal protection. Once

the protection is triggered, FF pulls to GND and

the corresponding fault bit is set to 1. After the IC

recovers from protection, FF releases to high

with a

750μs delay.

Open LED Protection

Open string protection is achieved through

detecting the voltage of OVP and LEDX. During

operation, if one string is open, the respective

LEDX voltage is low to ground, and the IC keeps

charging the output voltage until it reaches the

OVP threshold. If OVP has been triggered, the

chip stops switching and marks off the fault

string, which has an LEDX pin voltage below

100mV. Once marked, the remaining LED

strings force the output voltage back into normal

regulation. The string with the largest voltage

drop determines the output regulation value.

The mark-off string sends a 10

μs pulse current

to check whether an open fault is removed after

every 500

μs delay, so open string protection is

recoverable.

Short String Protection

The MP3367 monitors the LEDX voltages to

determine whether a short string fault has

occurred. When one or more strings are shorted,

the respective LEDX pins tolerate high voltage

stress. If an LEDX voltage exceeds the short

protection threshold, an internal counter starts.

When this fault condition lasts for 7.7ms (DPWM =

100%), the fault string is marked off. Once a

string is marked off, it disconnects from the

output voltage loop until the short is removed.