ADP5501 datasheet(11/28 Pages) AD

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ADP5501

Rev. 0 | Page 11 of 28

MAX

DIM

BACKLIGHT

CURRENT

BL_EN = 1 DIM_EN = 1

DIM_EN = 0 BL_EN = 0

Figure 18. Backlight Turn-On/Turn-Off/Dim

The maximum and dim settings can be set between 0 mA and

30 mA; therefore, it is possible to program a dim setting that is

greater than a maximum setting. For normal expected opera-

tion, the user should program the dim setting to less than the

maximum setting.

AUTOMATIC DIM AND TURN-OFF TIMERS

The user can program the backlight to dim automatically by

using the BL_DIMT timer in Register 0x03. The dim timer has

15 settings ranging from 10 sec to 2 min. The user should

program the dim timer before turning on the backlight. If

BL_EN = 1, the backlight turns on to its maximum setting, and

the dim timer starts counting. When the dim timer expires, the

internal state machine sets DIM_EN = 1, and the backlight goes

to its dim setting.

MAX

DIM

BACKLIGHT

CURRENT

BL_EN = 1

BL_EN = 0

DIM_EN = 1

DIM_EN = 0

BL_EN = 1

DIM_EN = 1

DIM TIMER

RUNNING

DIM TIMER

RUNNING

SET BY USER

SET BY INTERNAL STATEMACHINE

Figure 19. Dim Timer

If the user clears the DIM_EN bit (or reasserts the BL_EN bit),

the backlight reverts to its maximum setting, and the dim timer

begins counting again. When the dim timer expires, the internal

state machine again sets DIM_EN = 1, and the backlight goes to

its dim setting. Reasserting BL_EN at any point during the dim

timer countdown causes the timer to reset and begin counting

again. The backlight can be turned off at any point during the

dim timer countdown by clearing BL_EN.

The user can also program the backlight to turn off automatic-

ally by using the BL_OFFT timer in Register 0x03. The off timer

has 15 settings ranging from 10 sec to 2 min. The user should

program the off timer before turning on the backlight. If

BL_EN = 1, the backlight turns on to its maximum setting, and

the off timer starts counting. When the off timer expires, the

internal state machine clears the BL_EN bit, and the backlight

turns off.

MAX

BL_EN = 1 BL_EN = 0

BACKLIGHT

CURRENT

OFF TIMER

RUNNING

SET BY USER

SET BY INTERNAL STATE MACHINE

Figure 20. Off Time

Reasserting BL_EN at any point during the off timer count-

down 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.

MAX

DIM

BL_EN = 1

BL_EN = 0

DIM_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 effect on the eyes of near instant turn-

on and turn-off of the backlight, the ADP5501 contains timers

to facilitate smooth fading among the off, on, and dim states. By

default (BL_LAW = 00 in Register 0x02), the ADP5501

implements a fading scheme using the linear backlight code

algorithm (see Equation 1).

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