MP4652—HIGH PERFORMANCE OFF-LINE TV LED DRIVER

MP4652 Rev.1.01

www.MonolithicPower.com

6

9/23/2011

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PIN FUNCTIONS

Pin #

Name

Description

1

OVP

Over Voltage Protection. The output voltage is sensed by this pin through a voltage divider. If

the voltage at OVP exceeds 2.38V for 7µs, the Fault Mode is triggered.

2

SYNC

Synchronization. For burst dimming frequency. Application of a narrow-pulse synchronizing

signal on this pin will synchronize the burst frequency on BFS pin. The frequency of the

synchronizing signal should be higher than the frequency set by BFS pin.

3

SSD

Short String Detection. A comparator is integrated in this pin for short string protection. If the

voltage on this pin falls below 2.36V for 7µs, the Fault Mode is triggered.

4

FB

LED Current Feedback Input. The average voltage at this pin is regulated to 0.6V by an

internal error amplifier.

The voltage on this pin is also used for short string detection. When the voltage on this pin

goes higher than 1.2V for 7µs, the IC recognizes this as short string condition and triggers

the Fault Mode.

For fixed-operating–frequency PWM-controlled applications—such as half-bridge, flyback or

other topologies—shunt a current-sensing resistor from the cathode of the LED to ground

and use a sample-hold circuit to feed the LED current to FB pin. The sample-hold circuit

should hold the sensed current value on FB pin at PWM off interval.

For frequency controlled applications, like the LLC topology, the LED current is regulated

through an external amplifier, pull FB to ground and let IC operate with maximum duty cycle.

5

COMP

Feedback Compensation Node. For fixed-operating–frequency PWM-controlled applications,

connect a compensation capacitor or an R-C network from this pin to GND.

For frequency controlled applications, like the LLC topology, connect a 1nF cap on this pin.

6

FT

Fault Timer. Connect a timing capacitor from this pin to GND to set the fault timer to recover

the system. When the voltage on this pin goes higher than the 2.38V threshold, the IC

recovers.

If the system requires a latch up for Fault Mode, connect a resistor smaller than 250kΩ to this

pin.

7

PWMOUT

PWM Dimming Control Output. This pin outputs the PWM dimming driver signal to the LED

dimming MOSFET for fast PWM dimming. In Fault Mode PWMOUT is pulled low.

8

FSET

Frequency Set. The source current through this pin determines the operating frequency of

the MP4652.

For fixed-operating–frequency PWM-controlled applications, connect a resistor from this pin

to GND to set the operating frequency. For typical applications, a 25kΩ resistor sets the

operating frequency at 50kHz.

For frequency controlled applications (like LLC), apply the control voltage (the output of the

regulation loop) to this pin through a resistor. This control voltage programs the source

current through the FSET pin and thus controls the operating frequency.

9

BFS

Burst Frequency Set. For DC input PWM dimming. Connect a resistor in parallel with a

capacitor from BFS to GND. The resistor and capacitor programs the burst frequency.

For direct PWM input PWM dimming, pull up BFS to VCC with a 20kΩ resistor and apply the

PWM signal to the PWMIN pin.

10

PWMIN

PWM Dimming Control Input. For DC input PWM dimming, the voltage range from 0 V to

1.2V at PWMIN linearly sets the PWM dimming duty cycle from 0 to 100%.

For direct PWM input PWM dimming, directly apply the PWM signal on this pin. The MP4652

has positive dimming polarity.