MP24894 – STEP-DOWN LED-CURRENT CONTROLLER WITH WIDE 6V TO 60V INPUT VOLTAGE

MP24894 Rev 1.01

www.MonolithicPower.com

9

12/20/2012

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© 2012 MPS. All Rights Reserved.

OPERATION

Steady State

The MP24894 is a step-down LED-current

controller with hysteresis control that is easily

configured for a wide input that ranges from 6V to

60V input. The MP24894 uses a high-side

current-sense resistor to detect and regulate

LED current. The voltage across the current-

sense resistor is measured and regulated in the

200mV±30mV range.

The internal 1.18V reference voltage provides a

0.3V reference to enable the part. When

and enables the other blocks. The MP24894 also

provides a 5V pull-up voltage as current reference

voltage when EN/DIM pin is float.

The inductor current is sensed through the

R2 (see Figure 1) is shorted and inductor current

upper-threshold is fixed by R1. When the switch is

off, inductor current lower-threshold is fixed by R1

and R2. The ratio of R1 and R2 determines the

current hysteresis.

System Soft Start

The voltage on the EN/DIM pin provides the

inductor current reference. An external capacitor

from the EN/DIM pin to ground provides a

source charges the capacitor from 0V to 5V to

fulfill soft-start function.

Dimming Control

The MP24894 allows the EN/DIM pin to control

both Analog and PWM dimming. Whenever the

voltage on DIM is less than 0.25V, the chip turns

off. For analog dimming, when the voltage on DIM

is from 0.3V to 2.7V, the LED current will change

from 20% to 100% of the maximum LED current.

If the voltage on EN pin is higher than 2.9V,

output LED current will equal the maximum LED

current. For PWM dimming, the signal amplitude

must exceed 3V. Choose a PWM frequency in

range of 100Hz to 20kHz for good dimming

linearity.