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

MP4655 Rev 1.0

www.MonolithicPower.com

21

2/2/2016

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output to drive the dimming MOSFET directly,

which helps achieve fast and high-contrast ratio

PWM dimming.

The MP4655 achieves a 1000:1 PWM dimming

ratio at 200Hz PWM dimming frequency (0.1%

minimum PWM dimming duty). The PWM

dimming ratio may decrease with a higher PWM

dimming frequency.

For analog dimming mode, a DC voltage on

ADIM or a pulse signal on ADIMP can be used.

For DC input analog dimming, apply a DC analog

signal from 0V to 2.4V on ADIM to dim the LED

current amplitude from 0 to 100%. ADIMP can be

left open or pulled high to VCC through a 100kΩ

resistor in this mode.

For analog dimming with a pulse input signal,

apply the pulse signal on ADIMP and a 100nF

capacitor on ADIM, depending on the frequency

of this pulse signal. The duty cycle of this pulse

signal from 0 to 100% dims the LED current from

0 to 100%.

The PWM dimming and analog dimming could be

applied to the IC simultaneously for an extra

dimming ratio.

Protection Features

The MP4655 integrates sufficient protection for

the LLC power stage, the output system voltage

stage, and the LED driver stage.

Capacitive Mode Protection for the LLC

Power Stage

The MP4655 integrates individual capacitive

mode protection for the LLC power stage by

detecting the secondary side signal. Feed back

the secondary side winding voltage to CMODE

for capacitive mode protection. When capacitive

mode is detected, the MP4655 discharges the

SS voltage and increases the LLC operating

frequency. If the capacitive mode is still detected

when the operating frequency is higher than the

threshold frequency setting by FTH_CMODE, the

IC latches up and outputs a high fault indicator.

System Voltage Stage Protection

The protections for the system voltage stage

include over-system voltage protection, short

protection, and open-feedback loop protection.

1. Over-system voltage protection

VFB senses the output system voltage for

regulation and over-voltage protection. If the VFB

triggers the over-system voltage protection and

latches up. The fault indicator output is high.

2. System voltage stage short protection

VOCP senses the current through the output

system voltage stage for short protection of the

system voltage stage. If the voltage on VOCP is

lower than -203mV for 7µs, the MP4655 latches

up and outputs a high fault indicator.

3. System

voltage

stage

open-feedback

protection

During the PWM dimming off interval, if the VFB

voltage is lower than 50% of its reference and

VCOMP is saturated for 512 switching cycles, the

IC latches up and outputs a high fault indicator.

During the PWM dimming on interval, if the VFB

voltage is lower than 50% of its reference voltage

and DCOMP is high for 512 cycles, the IC

latches up and outputs a high fault indicator.

LED Driver Stage Protection

The fault protection for the LED driver stage

includes the open LED protection, short LED

protection, over-LED current protection, open

feedback loop protection, and protection for any

point of the LED string shorting to ground.

The voltage of the LED strings is sensed on

VLED1 and VLED2. Both the maximum value

and the difference in voltages of VLED1 and

VLED2 are used for protection. When the

maximum value of VLED1 and VLED2 rises

higher than 2.41V or the difference in the

voltages rises higher than 150mV for 8µs, the IC

triggers over-LED voltage protection (the voltage

difference can be adjusted by the external input

resistance on VLED1 or VLED2).

DIMO is pulled low, and the output system

voltage is regulated by the LLC frequency control,

the same as in PWM off condition, and the fault

indicator output is high. If the maximum value of

VLED1 and VLED2 rises higher than 3V for 7.6µs,

the MP4655 latches up and disables the LLC

power stage to avoid any damage to the LED

driver stage. The fault indicator output is high.

The secondary side current of the LED driver

stage is sensed on IOCP/FAULT. When the