MP3394—4-STRING, MAX 200mA/STRING WHITE LED DRIVER

MP3394 Rev. 1.07

www.MonolithicPower.com

10

3/21/2013

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When bias the BOSC pin to a DC level by a

resistor, applying an external PWM signal to the

DBRT pin to achieve the external PWM dimming.

A DC analog signal can be directly applied to the

DBRT pin to modulate the LED current with a

capacitor on BOSC pin. And the DC signal is

then converted to a DPWM dimming signal with

the setting oscillation frequency.

The brightness of the LED array is proportional to

the duty cycle of the DPWM signal. The DPWM

signal frequency is set by the cap at the BOSC

pin.

Open String Protection

The open string protection is achieved through

detecting the voltage of OVP and LED1~4 pin. If

one or more strings are open, the respective

LEDX pins are pulled to ground and the IC keeps

charging the output voltage until it reach OVP

threshold. Then the part marks off the open

strings whose LEDX pin voltage is lower than

196mV. Once the mark-off operation completes,

the remaining LED strings force the output

voltage back into tight regulation. The string with

the highest voltage drop is the ruling string during

output regulation.

The MP3394 always tries to light at least one

string and if all strings are open, the MP3394

shuts down the step-up converter. The part

maintains mark-off information until resetting it.

Short String Protection

The MP3394 monitors the LEDX pin voltage to

judge if the short string fault occurs. If one or

more strings are short, the respective LEDX pins

tolerate high voltage stress. If the LEDX pin

voltage is higher than 6.3V, the short string

condition is detected on the respective string.

When the short string fault (LEDX over-voltage

fault) keeps for 2048 switching clocks, the fault

string is marked off and disable. Once a string is

marked off, its current regulation is forced to

disconnect

from

the

output

voltage

loop

regulation. The marked-off LED strings will be

shut off totally until the part restarts. If all strings

are short, the MP3394 will shut down the step-up

converter.

The

part

maintains

mark-off

information until resetting it.