MP24893 – STEP DOWN WLED DRIVER WITH WIDE 6V-TO-36V INPUT VOLTAGE

MP24893 Rev.1.02

www.MonolithicPower.com

7

12/7/2012

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OPERATION

Steady State

The MP24893 is a hysteretic-controlled, step-

down LED driver that is easily configured for

various applications with an input range from 6V

to 36V. The converter employs a high-side

current-sense resistor to detect and regulate the

LED current. The voltage across the current-

sense resistor is measured and regulated to

within 202mV±30mV.

The internal 1.275V reference voltage provides a

0.2V reference to enable the part and a 1.275V

pull-up voltage as current reference. When

and the other blocks are enabled.

current. When the switch is on, R2 is shorted and

R1 sets the output current upper-threshold.

When the switch is off, R1 and R2 set the output

current lower-threshold, and the ratio of R1 and

R2 determines the current hysteresis.

Enable Control

Once Input voltage is applied, the internal 1.275V

reference is connected to EN/DIM pin through

pull up resistor. If the EN/DIM pin is left open, the

IC will automatically start up to the maximum

brightness. Adding a capacitor to this pin can

hereby program a soft-start time.

Applying an external voltage range from 0.2V to

1.25V to the EN/DIM pin linearly controls the

current-sense voltage reference from 0mV to

202mV for analog dimming.

Applying an external PWM voltage with an

amplitude of 1.25V to the EN/DIM pin achieves

PWM dimming. For additional information 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 is the inductor

current reference. An external capacitor from the

EN/DIM pin to ground provides a soft-start delay.

the capacitor from 0V to 1.25V for soft-start.

Dimming Control

MP24893 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-to-2.5V DC voltage to this pin.