Diodes AL8808 - Manual (Page 11)

NEW PROD
UC
T
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
ng (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
w
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
PWM Frequenc
mming accuracy c
11 of 20
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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
m
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
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
© Diodes Incorporate
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
3
ed
ll
At
g
s
g
s
d
or