MP4653—REAL LIPS CC/CV MODE LLC TV LED DRIVER

MP4653 Rev 1.01

www.MonolithicPower.com

17

6/28/2012

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© 2012 MPS. All Rights Reserved.

of the voltage-loop error amplifier is pulled low

at PWM on interval.

MP4653 also integrates burst mode for the

voltage regulation. When VFB voltage is higher

than 1.1 times of the reference voltage and the

VCOMP voltage is sufficiently low (which

means a highest operating frequency), the IC

skips some switching cycles until VFB voltage

decreases sufficiently.

The operating frequency is controlled by the

larger one of the outputs of the current-loop

error amplifier and the voltage-loop error

amplifier. A high compensation output voltage

gets a low operating frequency.

Dimming Control

The MP4653 provides two dimming methods:

PWM Dimming Mode and Analog Dimming

Mode. Applying a digital PWM signal on the

PWMIN pin allows the PWM dimming. The

brightness of the LED string is proportional to

the duty cycle of the external PWM signal. A

driving signal on PWMOUT pin is output to

directly drive the dimming MOSFET, which

helps to achieve fast and high contrast ratio

PWM dimming.

MP4653 achieves 500:1 PWM dimming ratio

(0.2% minimum PWM dimming duty) at 200Hz

PWM dimming frequency. The PWM dimming

ratio may decrease with a higher PWM dimming

frequency.

A DC analog signal from 0V to 1.18V on A-Dim

pin dims the LED current amplitude from 0 to

100%.

For PWM and analog dimming control, apply

the PWM dimming signal on PWMIN pin and

apply the analog dimming signal on A-dim pin.

Bus Voltage Stage Protection

The MP4653 features rich and smart protection

to increase system reliability. It protects the

fault condition at both the DC bus voltage stage

and the LED driver stage.

The protection for the DC bus voltage stage

includes the over voltage protection and over

current protection (short protection).

The VFB pin senses the bus stage voltage for

voltage regulation and also for over voltage

protection. When the VFB pin voltage gets

higher than 2.4V for 2us, IC triggers the Bus

Voltage Stage Protection.

The secondary side current of bus voltage

stage is sensed on VOCP pin. When VOCP

voltage gets lower than -100mV, IC triggers the

Bus Voltage Stage Protection.

At Bus Voltage Stage Protection, the whole

gate driving signals are disabled and no power

is delivered to the output, including both the DC

bus voltage stage and the LED driver stage.

The current loop compensation node ICOMP

pin and the soft start SS pin are pulled low. The

hiccup timer for the bus voltage stage starts.

The voltage-loop compensation node VCOMP

pin is disconnected from the internal amplifier

and holds its value until the fault condition

disappears. A 2μA current source charges the

VCOMP pin capacitor till VCOMP voltage hits

3V, and then a 2μA current source discharges

VCOMP pin until 0.45V and then the system

recovers.

LED Driver Stage Protection

The fault protection for the LED driver stage

includes the open LED protection, short LED

protection, over LED current protection and any

point of LED string short to ground protection.

The voltage of the LED strings are sensed on

VLED1~VLED4 pins. The maximum value of

VLED1~VLED4 and their voltage difference are

used for protection. When the maximum value

of VLED1~VLED4 gets higher than 2.4V or their

voltage difference get larger than 150mV (this

value can be adjusted by the external input

resistance on VLED# pins), IC triggers the LED

Driver Stage Protection.

The LED current feedback IFB is also used for

over LED current protection. When IFB voltage

gets higher than 300mV for 200us or when IFB

voltage gets higher than 600mV, IC triggers the

LED Driver Stage Protection.

The secondary side current of the LED driver

stage is sensed on SSD pin. When SSD pin

voltage gets lower than -200mV for 2us, IC

triggers the LED Driver Stage Protection.

At the LED Driver Stage Protection, the driving

signal for the dimming MOSFET is disabled to