MP4652—HIGH PERFORMANCE OFF-LINE TV LED DRIVER

MP4652 Rev.1.01

www.MonolithicPower.com

11

9/23/2011

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© 2011 MPS. All Rights Reserved.

APPLICATION INFORMATION

Pin 1 (OVP):

This pin is used for over-voltage protection.

When the output voltage to this pin exceeds

2.38V for 7μs, the Fault Mode is triggered. For

applications involving multiple LED strings, apply

the maximum output voltage of the LED strings to

this pin.

Pin 3 (SSD):

This short string detection pin is used for

protection against shorts along any point of the

LED string to ground. The SSD pin monitors the

secondary side current. When the voltage on this

pin falls below 2.36V for 7μs, the IC treats the

condition as a short and triggers the Fault Mode.

Pin 4 (FB):

This pin is used for LED current regulation. The

voltage on this pin is regulated by an external

circuit with a 0.6V average value. Use a sample-

hold circuit to sense the LED current when the

PWM goes high, and hold the value when the

PWM goes low.

The FB pin also functions as short string

protection. When the voltage on FB exceeds

1.2V for 7μs, the IC triggers the Fault Mode.

For frequency-controlled application like an LLC

power stage, the LED current is regulated with an

external-frequency control loop. Connect FB to

ground and set the IC to operate at the maximum

duty cycle.

Pin 5 (COMP):

This pin is used for compensation purposes. For

PWM-controlled applications, such as half-bridge

and flyback power stages, connect an X7R

ceramic capacitor with a value between 47nF and

470nF from COMP to GND. The value of this

capacitor determines the stability of the LED

current regulation.

For frequency-controlled applications like the

LLC power stage, connect a 1nF capacitor to the

COMP pin.

Pin 6 (FT):

Connect a capacitor from this pin to GND to set

the fault timer. This sets the system recovery

time after detecting a fault condition.

A

C

V

T

FT

FT

μ

8

38

.

2

×

=

A 10nF capacitor on FT sets the delay time to

around 3ms

If the circuit requires a latch-up for Fault Mode,

connect this pin to a 200kΩ resistor.

Pin 8 (FSET):

This pin is used to set the operating frequency.

The source current through this pin determines

the operating frequency.

For fixed-operating–frequency PWM-controlled

applications—like half-bridge and flyback power

stages—connect a resistor from this pin to GND

o

FSET

f

R

9

10

25

.

1

×

=

25kΩ.

For frequency-controlled applications like LLC,

connect the control voltage to FSET pin through

a resistor, as shown in Figure 3. This control

voltage programs the source current through this

pin to control the operating frequency.

FSET

MP4652

Figure 3—FSET Set Up for Frequency

Controlled Application.