MP24833 – 3A, 55V WHITE LED DRIVER

MP24833 Rev. 1.0

www.MonolithicPower.com

7

05/05/2010

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PIN FUNCTIONS

Pin #

Name

Description

1

VDD

Supply Voltage. The MP24833 operates from a 4.5V to 55V unregulated input (with respect to

VSS). Input capacitor is needed to prevent large voltage spikes from appearing at the input.

2

VSS,

exposed

pad

Power Return. Connect to the lowest potential in the circuit, which is typically the anode of the

Schottky rectifier. This pin is the voltage reference for the regulated output voltage, and thus

requires extra care in layout. The exposed pad is also connected to this pin

3

OVP

Over-Voltage Protection. Use a voltage divider to program the OVP threshold. When the OVP

pin voltage reaches the shutdown threshold of 1.2V, the switch turns off and will recover

when the OVP voltage drops to normal operating range. When the voltage (with respect to

VSS) drops below 0.2V and the FB pin voltage is less than 0.1V, the chip treats this as a

short circuit and the operating frequency folds back. Program the OVP pin voltage from 0.2V

to 1.2V for normal operation.

4

FB

LED Current Feedback Input. Senses the current across the sensing resistor between FB and

VSS. Connect the current sensing resistor from the bottom of the LED strings to VSS. The FB

pin is connected to the bottom of the LED strings. The regulation voltage is 0.198V.

5

EN/DIM

On/Off Control Input and Dimming Command Input. A voltage greater than 0.67V will turn on

the chip. This pin implements both DC and PWM dimming. When the EN/DIM pin voltage

(with respect to INGND) rises from 0.67V to 1.36V, the LED current will change from 0% to

100% of the maximum LED current. To use PWM dimming, apply a 100Hz-to-2kHz square

wave signal with amplitude greater than 1.5V to this pin. For combined analog and PWM

dimming, apply a 100HZ to 2kHz square wave signal with amplitude from 0.67V to 1.36V.

6

INGND Input Ground Reference. This pin is the reference for the EN/DIM signal.

7

BST

Bootstrap. Connect a capacitor between SW and BST pin to form a floating supply for the

power switch driver. Use a 100nF or larger ceramic capacitor to provide sufficient energy to

drive the power switch with this supply voltage.

8

SW

Switch Output. Source of the internal MOSFET. Connect this pin to the power inductor and

the cathode of the rectifier diode.