MP24895A

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

MP24895A Rev. 1.0

www.MonolithicPower.com

12

2/3/2017

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t0

Tsw

PWM Signal

t1t2

Figure 4: PWM Dimming Waveforms

t0-t1: Delay time caused by the transistor

turning

off.

For

the

Q1

transistor

(i.e.:

MMBT3904), t1 is about 1µs - 2µs.

t1-t2:

Delay

time

caused

by

the

signal

transmission (less than 1µs).

The average LED current is proportional to the

duty cycle of the PWM signal. For optimal PWM

dimming linearity, the inductor current must

achieve the peak threshold during the PWM on

time. The minimum PWM duty cycle can be

estimated with Equation (3):

Dmin/fpwm=t1+t2+4*D*Tsw

(3)

PCB Layout Guidelines

Efficient

PCB

layout

is

critical

for

stable

operation. For best results, follow the guidelines

below.

the set current error.

2. Keep the input loop (including the input

capacitor,

Schottky

diode,

and

internal

MOSFET) as short as possible.