MP3391—8-CHANNEL, 120mA/CH STEP-UP WLED DRIVER CONTROLLER

MP3391 Rev. 1.11

www.MonolithicPower.com

11

3/14/2013

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Open String Protection

The open string protection is achieved through

detecting the voltage of OVP and LED1~8 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 less than

190mV. Once the mark-off operation completes,

the remaining LED strings will force the output

voltage back into tight regulation. The string with

the highest voltage drop is the ruling string during

output regulation.

The MP3391 always tries to light at least one

string and if all strings in use are open,

theMP3391 shuts down the step-up converter.

The part maintains mark-off information until

resetting it.

Short String Protection

The MP3391 monitors the LEDX pin voltage to

judge if the short string occurs. If one or more

strings are short, the respective LEDX pins

tolerate high voltage stress. If the LEDX pin

voltage is higher than threshold programmed by

SSET pin, the short string condition is detected

on the respective string. When the short string

fault (LEDX over-voltage fault) continues for

greater than protection timer programmed by

TSET capacitor, the string is marked off and

disabled. 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 in use are short, the MP3391 shuts

down the step-up converter.

When the open or short protection is triggered,

the FF pin will be pull to GND. the pull-up resistor

indicate the system status.