ADP5520 datasheet(13/40 Pages) AD

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ADP5520

Rev. 0 | Page 13 of 40

Figure 25 shows the fade timers used with the dim and off timers.

MAX

DIM

BL_EN = 1

BL_EN = 0

DIM_EN = 0

DIM_EN = 1

BACKLIGHT

CURRENT

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.

MAX

BL_EN = 1

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

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

FADE-IN TIME (s)

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

0.5

1.01.52.02.53.03.54.04.55.05.5

FADE-OUT TIME (s)

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

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