New prod uc t, Applicatio, On informat – Diodes AL8808 User Manual

Page 11: Tion, Al8808

NEW PROD

AL8808

Document number

Applicatio

PWM Dimmin

The CTRL pin is
output stage.

The ultimate PW
lower switching
the accuracy/line

At the start of e
threshold isn’t re

Greater PWM d
frequency.

The three figure
from a 12V rail a

Figure 36. 0

Figure 38. 0

As can be obse
value.

r: DS35648 Rev. 2

on Informat

(cont.)

s designed to be

WM dimming reso

frequencies and

earity of the PWM

each PWM cycle

eached then the

dimming dynami

s below show 0.

at +25°C for a no

.2% PWM Duty

68µH

.2% PWM Duty

22µH

rved from Figure

- 2

tion

(cont.)

e driven by both

olution is determ

/or higher PWM

M dimming.

e the LED curre

accuracy will be

c ranges can be

2% duty cycle P

ominal LED curre

Cycle at 100Hz

H Inductance

Cycle at 500Hz

H Inductance

e 37 greater dim

3.3V and 5V log

ined by the num

frequencies the

ent needs to res

greatly affected.

e achieved by r

PWM pulse resol

ent of 670mA

PWM Frequenc

mming accuracy c

11 of 20

www.diodes.co

gic levels directly

ber of full LED s

number of full sw

start from zero u
.

reducing the PW

ution with differe

cy and

Fig

cy and

can be achieved

y from a logic ou

switching cycles t

witching cycles t

up to the upper

WM dimming fre

ent PWM frequen

gure 37. 0.2% P

d by reducing bo

tput with either a

that can be achie

r threshold level

quency and/or i

ncies and differe

WM Duty Cycle

22µH Indu

th the PWM dim

an open drain ou

eved during the

eved is reduced

(nominally 120

ncreasing the A

nt inductor value

e at 100Hz PWM

uctance

mming frequency

January 201

AL8808

utput or push pu

PWM on-time. A

thereby reducing

mV/R

SET

). If this

AL8808 switching

es driving 2 LEDs

Frequency and

and the inducto