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

MP4653 Rev 1.01

www.MonolithicPower.com

22

6/28/2012

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control the starting operation of the IC, use this

“Enable” signal to control this supply input

voltage with following circuit in figure 4.

Figure 4—MP4653 Enable control circuit

PWM

dimming

signal

output

(Pin

16,

PWMOUT)

This pin outputs a PWM dimming signal to drive

the external dimming MOSFET (MN) in series

with the LED string, and achieves fast PWM

dimming. Connect a resistor in series with this

pin to adjust the driving speed.

The PWMOUT signal is also used to control the

external P-MOS (MP) for protection, as shown in

figure 5A. Figure 5B shows the operating scheme

of this driving circuit. A negative voltage source (-

Vbus) is generated from the secondary winding

generated through the PWMOUT signal. By

pulse waveform with a negative magnitude is

generated on “P_Drive” (the P-MOS gate) and is

used to drive the P-MOS.

MP4653

PWMOUT

15

.

.

.

IFB

OVP

PWMOUT

OCP

VOCP

VFB

Vbus

Vbus

PWMOUT

MN

MP

Primary LLC

power stage

-Vbus

P_Drive

PWMOUT

Figure 5A—PWMOUT for the P_MOS Driver

Figure 5B—Scheme of the PWMOUT Driving

the P_MOS

Gate Driver Supply (Pin 17, VCC)

This pin supplies the gate drive signals GL,GR

and PWMOUT. Bypass this pin with a 1uF or

larger ceramic capacitor. This pin could also be

used to supply an external circuit.

Gate Drive Signals (Pin 18,20 GL,GR)

GL and GR provide the driving signal for the

power stage. GL and GR are 180 degree phase

shifted gate drive signals. With the enhanced

drive capability, GL and GR can directly drive the

external MOSFET in the power stage through a

gate driving transformer.

The gate driving transformer also isolates the

primary power stage and the secondary control

circuit. Place a 2.2nF Y cap between the power

stage ground and the reference ground for the

control circuit to improve the EMI performance.