Datasheet

Data Sheet ADP8861
Rev. B | Page 15 of 40
30
0
5
10
15
20
25
0 1.000.750.500.25
CURRENT (mA)
UNIT FADE TIME
LINEAR
SQUARE
CUBIC 11
CUBIC 10
08391-016
Figure 30. Comparison of the Dimming Transfers Laws
BACKLIGHT TURN ON/TURN OFF/DIM
With the device in active mode (nSTBY = 1), the backlight can
be turned on using the BL_EN bit in Register 0x01. Before
turning on the backlight, the user should ensure that the
maximum and dim settings are programmed. The backlight
turns on when BL_EN = 1. The backlight turns off when
BL_EN = 0.
MAX
BL_EN = 1 BL_EN = 0
BACKLIGHT
CURRENT
08391-017
Figure 31. Backlight Turn On/Turn Off
While the backlight is on (BL_EN = 1), the user can change to
the dim setting by programming DIM_EN = 1 in Register 0x01.
If DIM_EN = 0, the backlight reverts to its maximum setting.
MAX
DIM
BL_EN = 1
DIM_EN = 1 DIM_EN = 0 BL_EN = 0
BACKLIGHT
CURRENT
08391-018
Figure 32. Backlight Turn On/Dim/Turn Off
AUTOMATIC DIM AND TURN OFF TIMERS
The user can program the backlight to dim automatically by
using the DIMT bits in Register 0x07. The dim timer has
127 settings ranging from 1 sec to 127 sec. Program the dim
timer (DIMT) 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 enters its
dim setting.
MAX
DIM
BL_EN = 1 BL_EN = 0DIM_EN = 1 DIM_EN = 0 DIM_EN = 1
BACKLIGHT
CURRENT
DIM TIMER
RUNNING
DIM TIMER
RUNNING
SET BY USER
SET BY INTERNAL STATEMACHINE
08391-019
Figure 33. Dim Timer
If the user clears the DIM_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 enters its dim setting. 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 automati-
cally by using the OFFT bits in Register 0x06. The off timer has
127 settings ranging from 1 sec to 127 sec. Program the off
timer (OFFT) 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
07967-020
Figure 34. Off Timer
The backlight can be turned off at any point during the off
timer countdown by clearing BL_EN.