Datasheet

ADP5520
Rev. A | Page 12 of 40
Reasserting BL_EN at any point during the off timer countdown
causes the timer to reset and begin counting again. The backlight
can be turned off at any point during the off timer countdown
by clearing BL_EN.
The dim timer and off timer can be used together for sequential
maximum-to-dim-to-off functionality. With both the dim and
off timers programmed, if BL_EN is asserted, the backlight turns
on to its maximum setting. When the dim timer expires, the
backlight changes to its dim setting. When the off timer expires,
the backlight turns off.
07445-012
MAX
DIM
BL_EN = 1 BL_EN = 0DIM_EN = 1
BACKLIGHT
CURRENT
DIM TIMER
RUNNING
OFF TIMER
RUNNING
SET BY USER
SET BY INTERNAL STATE MACHINE
Figure 21. Dim and Off Timers Used Together
LINEAR BACKLIGHT FADE IN AND FADE OUT
To counteract the abrupt visual effect of near instant turn-on
and turn-off of the backlight, the ADP5520 contains timers to
facilitate the smooth fading between off, on, and dim states. By
default (BL_LAW = 00), the ADP5520 implements a fading
scheme using the linear backlight code algorithm (see Equation 1).
The BL_FI timer in Register 0x04 can be used for smooth fade-in
transitions from low to high backlight settings, such as off-to-dim,
off-to-maximum, and dim-to-maximum. The BL_FI timer can be
programmed to one of 15 settings ranging from 0.3 sec to 5.5 sec.
The BL_FI timer should be programmed before asserting BL_EN.
30.0
27.5
25.0
22.5
20.0
17.5
15.0
12.5
10.0
7.5
5.0
2.5
0
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
FADE-IN TIME (s)
BACKLIGHT CURRENT (mA)
07445-013
0.3 SEC
0.6 SEC
0.9 SEC
1.2 SEC
1.5 SEC
1.8 SEC
2.1 SEC
2.4 SEC
2.7 SEC
3.0 SEC
3.5 SEC
4.0 SEC
4.5 SEC
5.0 SEC
5.5 SEC
Figure 22. Linear Fade-In Times
The time programmed in BL_FI represents the time it takes the
backlight current to go from 0 mA to 30 mA. Fading between
intermediate settings is shorter.
The BL_FO timer in Register 0x04 can be used for smooth fade-
out transitions from high to low backlight settings such as
maximum-to-dim and dim-to-off. The BL_FO timer can be
programmed to one of 15 settings ranging from 0.3 sec to 5.5 sec.
The BL_FO timer should be programmed before asserting BL_EN.
30.0
27.5
25.0
22.5
20.0
17.5
15.0
12.5
10.0
7.5
5.0
2.5
0
0 0.51.01.52.02.53.03.54.04.55.05.5
FADE-OUT TIME (s)
BACKLIGHT CURRENT (mA)
07445-014
0.3 SEC
0.6 SEC
0.9 SEC
1.2 SEC
1.5 SEC
1.8 SEC
2.1 SEC
2.4 SEC
2.7 SEC
3.0 SEC
3.5 SEC
4.0 SEC
4.5 SEC
5.0 SEC
5.5 SEC
Figure 23. Linear Fade-out Times
The time programmed in BL_FO represents the time it takes
the backlight current to go from 30 mA to 0 mA. Fading
between intermediate settings is shorter.
Figure 24 shows the fade timers in use. With BL_FI and BL_FO
programmed, if BL_EN is asserted, then the backlight fades in
to its maximum setting. If DIM_EN is asserted, then the backlight
fades out to its dim setting. If BL_EN is cleared, the backlight
fades out to off.
07445-015
MAX
DIM
BL_EN = 1 BL_EN = 0 BL_EN = 0 BL_EN = 0
BL_EN = 1 BL_EN = 1
DIM_EN = 1
BACKLIGHT
CURRENT
FADE-OUT FADE-IN
FADE-OUTFADE-IN
F
ADE-OUT
MAX-T
O-DIM
FADE-IN
OFF-TO-MAX
FADE-OUT
DIM-TO-OFF
SET BY USER
Figure 24. Backlight Turn On/Off/Dim with Fade Timers
During any point in a fade-out, if BL_EN is asserted, then the
backlight stops at its current fade-out position and begins
fading in.
The fade-in and fade-out timers can be used independently of each
other, that is, fade-in can be enabled while fade-out is disabled.
The fade timers can also be used with the off and dim timers.