MP4651—OFF LINE LED DRIVER

MP4651 Rev.1.0

www.MonolithicPower.com

9

1/13/2011

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Fault Protection

System fault management facilities include the

over voltage protection, short string protection

and a delay timer for system recovery.

The output voltage is monitored by the OVP pin

through a voltage divider. Once the voltage on

OVP pin exceeds 2.38V for 7us, the MP4651

recognizes this as open condition and triggers

Fault Mode.

The SSD pin is used for short string detection.

When the voltage on SSD pin gets lower than

2.36V for 7us, the MP4651 recognizes this as

short string condition and triggers the Fault Mode.

FB pin also functions as short string protection.

When the voltage on FB pin is higher than 1.2V

for 7us, the IC triggers the Fault Mode.

At Fault Mode, the outputs of the gate drivers GL

and GR are disabled, the PWMOUT signal is

pulled down and the COMP capacitor is

discharged by a 30uA sourcing current. The fault

timer is started. An 8uA current source charges

the FT capacitor, and when FT voltage hits 2.38V,

system recovers. It enables the output driving

signals, releases the COMP, resets the fault flag

and pulls down the FT pin.