ADP5501 datasheet(13/28 Pages) AD

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ADP5501

Rev. 0 | Page 13 of

30.0

27.5

25.0

22.5

20.0

17.5

15.0

12.5

10.0

7.5

5.0

2.5

FADE OVERRIDE

A fade override feature allows the BL_FI and BL_FO timers to

be overridden when the BL_EN bit is reasserted (by the user

setting the FOVR bit in Register 0x02) during a fade-in or fade-

out period and to set the backlight to its maximum setting.

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

FADE-OUT TIME (Sec)

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

MAX

BACKLIGHT

CURRENT

BL_EN = 1

BL_EN = 0

BL_EN = 1

(REASSERTED BY USER )

BL_EN = 1

(REASSERTED BY USER)

FADE-OUT

OVERRIDDEN

FADE-IN

OVERRIDDEN

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 appear visually abrupt.

For example, for a given fade-in time, the eye notices an initial

increase in brightness as backlight current is increased but

cannot perceive much more increase in brightness as backlight

current is increased to maximum.

The reason for this is that the eye perceives changes in light

when the brightness of the light source is changed logarithmically

(Weber-Fechner law). To provide a more natural fading exper-

ience 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 in Register 0x02.

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 (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

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

Figure 28. Square Law Fade-Out Times

ADVANCED FADING (CUBIC 1 AND CUBIC 2)

Two additional advanced settings in Register 0x02 are available

for fading the backlight brightness levels, Cubic 1 (BL_LAW = 10)

and Cubic 2 (BL_LAW = 11). As shown in the backlight bright-

ness control block diagram in Figure 14, linear fading and

square fading are implemented by ramping the 128 linear/square

algorithm codes at a fixed frequency over the duration of a

given fade-in/fade-out time.

Cubic fading is implemented by re-using the square algorithm

codes but ramping them with a clock source whose frequency

output increases as the sink current code increases (see Figure 29).

Cubic 1 and Cubic 2 have different frequency vs. code charac-

teristics.

BST

DARK_MAX

DAYLIGHT_MAX

DAYLIGHT_DIM

OFFICE_MAX

OFFICE_DIM

BL_VALUE

MUX

DARK_DIM

COUNTERS

AND

CONTROL

LOGIC

BL_DIMT

BL_FI

BL_FO

BL_EN

DIM_EN

BL_OFFT

BL_LAW

CLOCK

GENERATOR

BL_LVL

BL_SNK

Figure 29. Backlight Brightness Control (Cubic)

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