MP4652—HIGH PERFORMANCE OFF-LINE TV LED DRIVER

MP4652 Rev.1.01

www.MonolithicPower.com

10

9/23/2011

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PWM dimming ratio at a 120Hz PWM dimming

frequency without any audible noise issue (or

500:1 PWM dimming ratio at 300Hz PWM

dimming frequency).

PWMOUT

PWMIN

COMP

Gate

Figure 2— Fast and Continuous PWM

Dimming

Fault Protection

System fault management features include open

LED protection, short LED protection if at any

point the LED string shorts to ground, protection

against shorts along the LED string, and a delay

timer for system recovery.

The output voltage is monitored by the OVP pin

through a voltage divider. Once the open LED

condition occurs and the voltage on the OVP pin

exceeds 2.38V for 7μs, the MP4652 recognizes

this as open condition and triggers the Fault

Mode.

The SSD pin monitors the secondary side current.

If any point of the LED string is shorted to ground,

the secondary side current increases. When the

voltage on SSD pin falls below 2.36V for 7μs, the

MP4652 triggers the Fault Mode.

The FB pin can also function as short LED string

protection. When the voltage on FB pin is higher

than 1.2V for 7μs, the IC triggers the Fault Mode.

In Fault Mode, the outputs of the gate drivers GL

and GR are disabled, the PWMOUT signal is

pulled low, and the COMP

capacitor is

discharged by a 30μA current source. The fault

timer then starts. An 8μA current source charges

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

the system recovers. The IC enables the output

driver signals, releases the COMP, resets the

fault flag, and pulls down the FT pin.

If the design requires a latch up for the IC at

Fault Mode, connect a 200kΩ resistor on the FT

pin.