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

MP4653 Rev 1.01

www.MonolithicPower.com

16

6/28/2012

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

© 2012 MPS. All Rights Reserved.

OPERATION

The MP4653 is a CC/CV mode LLC TV LED

driver, especially designed for the real LIPS

structure for the large size TV LED backlighting.

Powered by 9V to 30V input supplies, the

MP4653 outputs two 180 degree phase shifted

driving signals for the external power stages. Its

enhanced 9V gate driver provides adequate

driving capability and can directly drive the

external MOSFETs through an external gate

driving transformer.

The MP4653 employs frequency control for

the LLC power stage. Both the LED current and

the bus voltage are controlled. Figure 1 shows

the block diagram of MP4653.

Internal Regulator

The MP4653 includes an internal linear

regulator VCC. It is the supply voltage for the

gate driver and also for the internal circuit. The

MP4653 features Under Voltage Lockout. The

chip is disabled until VCC exceeds the UVLO

threshold.

System Startup

When the MP4653 is powered up, the VCC is

charged up, and when it passes the UVLO

threshold, IC starts up. It resets the voltage

control loop, the current control loop and

discharges the soft start capacitor. The MP4653

enjoys a soft start up.

The MP4653 gets a 4.35V input UVLO

threshold, and it can start up directly from the

system 5V standby power supply. Please refer

to figure 2.

The PWM dimming signal controls the start up

of the LED driver stage. The system operates in

constant voltage mode and the DC bus voltage

is controlled before PWM signal applied.

CC/CV Mode Operation

The MP4653 integrates a constant voltage

control loop (CV) and a constant current control

loop (CC). Both the LED current of the LED

stage and the bus voltage of the bus voltage

stage are controlled. The PWM dimming signal

is used to distinguish these two modes. At

PWM on interval, the current control loop is

effective (CC mode) and the LED current is

regulated. At PWM off interval, the voltage

control loop is effective and the DC bus voltage

is controlled (CV mode).

For the current control loop for the LED current

regulation, the LED current is fed back to IFB

pin. The internal error amplifier regulates the

average value of IFB signal to the internal

200mV

reference

voltage.

Its

output

is

connected

to

the

external

current-loop

compensation network on ICOMP pin through

an inner switch S1. At PWM on interval, S1 is

on, and the output of the error amplifier is

connected

to

the

external

compensation

network on ICOMP pin. The LED current is

regulated by this control loop. At PWM off

interval, S1 is turned off, and the compensation

network on ICOMP is disconnected from the

error amplifier and holds its value until next

PWM on interval. The output of the error

amplifier is pulled low at PWM off interval.

MP4653 integrates burst mode for the LED

current regulation. When IFB voltage is higher

than 1.1 times of its reference voltage and the

ICOMP voltage is sufficiently low (which means

a highest operating frequency), the IC skips

some switching cycles until IFB voltage

decreases sufficiently.

For the voltage control loop for the bus voltage

regulation, the bus voltage is fed back on VFB

pin. MP4653 automatically samples the VFB

voltage at PWM on interval and uses it as the

reference for the voltage control loop. The

internal voltage-loop error amplifier regulates

the average value of the VFB voltage to this

reference voltage at PWM off interval. Its output

is connected to the external voltage-loop

compensation network on VCOMP pin through

an inner switch S2. At PWM off interval, S2 is

on, and the output of the voltage-loop error

amplifier

is

connected

to

the

external

compensation network on VCOMP pin. The bus

voltage is regulated by this control loop. At

PWM on interval, S2 is turned off, and the

compensation

network

on

VCOMP

is

disconnected from the error amplifier and holds

its value until next PWM off interval. The output