MP4652—HIGH PERFORMANCE OFF-LINE TV LED DRIVER

MP4652 Rev.1.01

www.MonolithicPower.com

12

9/23/2011

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

© 2011 MPS. All Rights Reserved.

Pin 7 (PWMOUT):

This pin outputs the PWM dimming signal to

drive the dimming MOSFET in series with the

LED string for fast PWM dimming. Connect this

pin to the gate of the dimming MOSFET through

a driver resistor.

Pin 10 (PWMIN):

This pin is used for PWM-dimming brightness

control. For DC-input PWM dimming, the DC

voltage controls the PWM dimming duty cycle on

the output. The signal should be filtered for optimal

operation. A voltage in the range of 0V to 1.2V on

PWMIN programs the PWM dimming duty cycle

from 0 to 100%.

For direct PWM input PWM dimming, pull BFS

high to VCC through a 20kΩ resistor, and

connect the PWMIN pin directly to the PWM

source. Logic High is PWM On and Logic Low is

PWM Off.

Pin 9 (BFS):

BFS pin is used to set the burst frequency for DC

input PWM dimming, using the waveform shown

frequency.

BFS

2.4V

3.55V

Burst dimming

signal

Burst Dimming Frequency

Rising time

Gate

Figure 4—PWM Dimming with DC Input

Voltage at PWMIN Pin

These values are determined as follows:

Set a percentage of the rising time, where:

Burst

rise

rise

f

t

D

×

=

k

D

k

R

rise

BFS

43

.

21

1

1

16

.

21

+

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

−

≈

405

.

0

1

×

×

−

=

BFS

Burst

rise

BFS

R

f

D

C

For direct PWM input PWM dimming, pull BFS

high to VCC through a 20kΩ resistor and apply

the PWM signal to PWMIN pin.

Pin 2 (SYNC):

This

pin

is

used

for

burst

frequency

synchronization to synchronize the DC input

PWM dimming frequency. Application of a small-

pulse

synchronizing

frequency

signal

will

synchronize the burst frequency.

SYNC

EN

FB

VCC

BFS

FSET

FT

GND

GL

PWMOUT

VIN

GR

OVP

PWMIN

COMP

1

2

3

4

5

6

7

8

MP4652

14

15

16

SSD

10

11

12

SYNC

Signal

9

REF

13

A

BFS

Burst dimming

signal

1.2V

3.55V

2.4V

SYNC

Signal

A

Figure 5—Synchronized DC Input

PWM Dimming and Schematic