Datasheet
ADP5520
Rev. A | Page 13 of 40
Figure 25 shows the fade timers used with the dim and off timers.
07445-016
MAX
DIM
BL_EN = 1 BL_EN = 0
DIM_EN = 0
DIM_EN = 1
BACKLIGHT
CURRENT
FADE-OUT
FADE-OUT
FADE-IN
DIM TIMER
RUNNING
OFF TIMER
RUNNING
SET BY USER
SET BY INTERNAL STATE MACHINE
Figure 25. Fade/Dim/Off Timers Used Together
FADE OVERRIDE
A fade override feature allows the BL_FI and BL_FO timers to
be overridden if the BL_EN bit is reasserted (either by the user
or due to a key press) during a fade-in or fade-out period, and
sets the backlight to its maximum setting. Fade override can be
activated by setting the FOVR bit in Register 0x02.
07445-017
MAX
BL_EN = 1 BL_EN = 0 BL_EN = 0
BL_EN = 1
(REASSERTED BY
USER OR A KEY PRESS)
BL_EN = 1
(REASSERTED BY
USER OR A KEY PRESS)
BACKLIGHT
CURRENT
FADE-OUT
OVERRIDDEN
FADE-IN
OVERRIDDEN
SET BY USER
Figure 26. Fade Override
ADVANCED FADING (SQUARE)
Although the default linear fade algorithm gives a smooth increase
and decrease in backlight current, the resulting increase and
decrease in brightness still appears visually abrupt. For example,
for a given fade-in time, the eye can notice an initial increase in
brightness as backlight current is increased, but cannot perceive
much more of an increase in brightness as backlight current is
increased to maximum.
The reason for this is that the eye, like all human senses, perceives
changes in light when the brightness of the light source is changed
logarithmically (Weber-Fechner law). To achieve a more natural
fading experience to the user, the fade timers can be used in
conjunction with the square law approximation backlight codes
(see Equation 2) by setting BL_LAW = 01.
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)
07445-018
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
0.3 SEC
0.6 SEC
0.9 SEC
1.2 SEC
1.5 SEC
1.8 SEC
Figure 27. Square Law Fade-In Times
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)
07445-019
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 28. Square Law Fade-Out Times