MP4651—OFF LINE LED DRIVER

MP4651 Rev.1.0

www.MonolithicPower.com

10

1/13/2011

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

© 2011 MPS. All Rights Reserved.

APPLICATION INFORMATION

Pin 1 (OVP):

Over Voltage Protection: This pin is used for over

voltage

protection.

The

output

voltage

is

monitored by this pin and when the voltage on

this pin exceeds 2.38V for 7us, the Fault Mode is

triggered.

Pin 3 (SSD):

Short String Detection: This pin is used for short

string protection, when the voltage on this pin

gets lower than 2.36V for 7us, the IC treats it as

short string condition and triggers the Fault

Mode.

Pin 4 (FB):

LED Current Feedback. This pin is used for LED

current regulation. The voltage on this pin is

regulated with 0.6V average value.

FB pin also functions as short sting protection.

When the voltage on FB gets higher than 1.2V

for 7us, the IC triggers the Fault Mode.

Pin 5 (COMP):

This pin is used for compensation. Connect a

1~47nF capacitor from COMP to GND. This cap

should be X7R ceramic. The value of this cap

determines the stability of the LED current

regulation.

Pin 6 (FT):

Connect a capacitor from this pin to GND to set

the fault timer. It sets the time to recover the

system when a fault condition is detected.

FT

FT

2.38V C

T

8uA

×

=

A 10nF capacitor on FT sets the delay time

around 3ms

Pin 8 (FSET):

Connect a resistor from this pin to GND to set the

resistor R1 is calculated by

9

o

1.25 10

R1

f

×

=

50kHz.

Pin 7 (PWMOUT):

This pin outputs the burst dimming signal to the

LED for fast PWM dimming. Connect this pin

directly to the gate of the dimming MOSFET in

series of the LED.

Pin 10 (PWMIN):

This pin is used for burst brightness control. For

DC input burst dimming, the DC voltage on this

pin controls the burst percentage on the output.

The signal is filtered for optimal operation. A voltage

ranging from 0 to 1.2V on PWMIN programs the

burst dimming duty cycle from 0 to 100%.

For direct PWM burst dimming, Pull BFS high to

VCC through a 20kΩ resistor and connect

PWMIN pin to a logic level PWM signal. Logic

High is Burst On and a logic Low is Burst Off.

Pin 9 (BFS):

BFS pin is used to set the burst dimming

dimming frequency, as shown in figure 3.

BFS

2.4V

3.55V

Burst dimming

signal

Burst Dimming Frequency

Rising time

Figure 3—Burst Mode with DC Input Voltage

at PWMIN Pin

These values are determined as follows:

Set a percentage of the rising time, where:

rise

rise

Burst

Dt

f

=

×

BFS

rise

1

R

21.16k

1

21.43k

D

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≈− +

⎜⎟

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