MP24895A

– 6V - 36V, STEP-DOWN, WHITE, LED DRIVER

MP24895A Rev. 1.0

www.MonolithicPower.com

10

2/3/2017

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© 2017 MPS. All Rights Reserved.

OPERATION

Steady State

The MP24895A is a hysteretic-controlled, step-

down LED driver that can be configured easily

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 within 100mV ± 20mV.

The internal 1.28V reference voltage provides a

0.2V reference to enable the part and a 1.28V

pull-up voltage as the current reference. When

goes high, 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. The ratio of R1

and R2 determines the current hysteresis.

Enable Control

Once the input voltage is applied, the internal

1.28V

reference

is

connected

to

EN/DIM

through the pull-up resistor. If EN/DIM is left

open, the IC starts up automatically to the

maximum

brightness.

Add

a

capacitor

to

EN/DIM to program a soft-start time.

Apply an external DC voltage to EN/DIM to

control the current-sense voltage reference

linearly for analog dimming. Apply an external

pulse-width modulation (PWM) voltage with an

amplitude of 1.28V to EN/DIM to achieve PWM

dimming. For additional information on the

flexible external PWM dimming method, please

refer to the Selecting the Dimming Control

Mode section on Page 11.

System Soft Start

The voltage on EN/DIM is the inductor current

reference. An external capacitor from EN/DIM

starts up, the internal voltage source charges

the capacitor from 0V to 1.28V for soft start.

Dimming Control

The MP24895A provides two dimming methods:

PWM dimming and DC analog dimming.

To use PWM dimming, apply a square wave to

EN/DIM. To use analog dimming, apply a 0.3V

to 2.5V DC voltage to EN/DIM to control the

LED current range linearly from 25% to 200%.