MP24892 – STEP DOWN WLED DRIVER WITH WIDE 6V–45V INPUT VOLTAGE

MP24892 Rev. 1.0

www.MonolithicPower.com

7

11/3/2011

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OPERATION

Steady State

The MP24892 is a hysteretic-controlled step-

down LED driver that is easily configured for

various applications with an input range of 6V–

45V. The converter employs a high-side current

sensing resistor to detect and regulate the LED

current. The voltage across the current sensing

resistor is kept measured and regulated in

202mV±30mV range.

The internal 1.275V reference voltage provides a

0.2V reference to enable the part and a 1.275V

pull-up voltage as the current reference. When

and the other blocks are enabled.

Output current is sensed through a high-side

internal resistor R2 shorts out and R1 determines

the output current upper-threshold. When the

switch is off, R1 and R2 determine the output

current lower-threshold. The ratio of R1 and R2

determines the current hysteresis.

Enable Control

Once the input voltage is applied, a 2µA current

is sourced out from EN/DIM pin. If EN/DIM is left

open, the IC will automatically start up to the

maximum brightness. Applying a capacitor on

this pin programs a soft start time.

Applying an external voltage in the range of 0.2V

to 1.25V to this pin linearly controls the current

sensing voltage reference from 0mV to 202mV

for analog dimming.

Applying an external PWM signal with an

amplitude of approximately 1.25V to this pin

enables PWM dimming. For more on the flexible

external PWM dimming method, please refer to

the selecting dimming control mode section.

System Soft-Start

The voltage on the EN/DIM pin functions as the

inductor current reference. An external capacitor

from the EN/DIM pin to ground provides a soft-

source charges the capacitor from 0V to 1.25V.

Dimming Control

MP24892 provides two dimming methods: PWM

dimming and DC analog dimming.

To use PWM dimming, apply a square wave to

the EN/DIM pin. To use analog dimming, apply a

0.3V–2.5V DC voltage to this pin.