MP3388S—50V, 8-STRING, WHITE LED DRIVERS

MP3388S Rev.1.01

www.MonolithicPower.com

11

10/29/2012

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Open-String Protection

The open string protection is achieved through

over-voltage protection (OVP). If one or more

strings are open, the device pulls the respective

LEDx pins to ground and the output voltage

continues rising until it reaches the OVP

threshold. Then the device records and disable

the open LEDx strings with pin voltages less than

175mV. Once recording completes, the remaining

LED strings force the output voltage back into tight

regulation. The string with the highest voltage

drop determines the output regulation level.

The MP3388S will always try to light at least one

string. If all strings in use are open, the MP3388S

shuts down the step-up converter. The part

retains low-voltage LEDx string information until

the part shuts down.

Short-String Protection

The MP3388S monitors each LEDx pin voltage to

determine if there is a short string. If one or more

strings are shorted, the respective LEDx pins will

be pulled up to the boosted output and tolerate

high voltage stress. If the LEDx pin voltage

exceeds 5.5V, the device treats this condition as a

short string fault (LEDx over-voltage fault). If the

voltage remains above 5.5V more than than

and disables it. Once a string is recorded as a

short, its current regulation is forced to disconnect

from the output voltage loop regulation. The

recorded LED strings remain OFF until the part

restarts. If all strings in use are shorted, the

MP3388S shuts down the step-up converter.