MP4655–PURE, SINGLE-STAGE, LLC, LED CURRENT AND SYSTEM VOLTAGE CONTROLLER

MP4655 Rev 1.0

www.MonolithicPower.com

22

2/2/2016

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IOCP voltage is lower than -320mV for 7µs, the

MP4655 triggers the LED driver stage protection.

At the LED driver stage protection, the DIMO is

pulled low, and the output system voltage is

regulated by the LLC frequency control, the same

as in PWM off condition. The fault indicator

output is high after 270µs. After the LED driver

stage protection is triggered, IOCP/FAULT

continues detecting the LED driver stage current.

If the voltage on IOCP/FAULT remains lower

than -320mV for 270µs, the MP4655 latches up

and disables the LLC power stage.

The LED current feedback (IFB) is used for over-

LED current protection. When IFB voltage rises

higher than 415mV for 340µs or the IFB voltage

rises higher than 555mV for 6µs, the IC triggers

the LED driver stage protection.

If the voltage on IFB is lower than 50% of its

reference voltage, and the ICOMP is saturated

for 1024 cycles, the IC considers this to be a

short LED to GND protection or open feedback

protection and triggers the LED driver stage

protection.

The

reference

voltage

varies

according to the analog dimming signal.

In a fault condition of the LED driver stage, the

gate driving signals for the LLC power MOSFETs

are still active and the output system voltage is

regulated, only if the LED driver stage can be

disconnected from the power stage. Therefore,

the system power supply is not influenced by the

fault protection of the LED driver stage. A

MOSFET can be used to disconnect the LED

driver stage at the LED fault condition (see

Figure 11).

Thermal protection is also integrated in the

MP4655.