Datasheet

ADP5520
Rev. A | Page 11 of 40
BACKLIGHT TURN ON/OFF/DIM
With the device in operating mode (nSTNBY = 1), the backlight
can be turned on using the BL_EN bit in Register 0x00. Before
turning on the backlight, the user should choose which level
(daylight (L1), office (L2), or dark (L3)) to operate in, and ensure
that maximum and dim settings are programmed for that level.
The backlight turns on when BL_EN = 1. The backlight turns
off when BL_EN = 0.
07445-008
MAX
BL_EN = 1 BL_EN = 0
BACKLIGHT
CURRENT
Figure 17. Backlight Turn On/Off
While the backlight is on (BL_EN = 1), the user can make it
change to a dim setting by programming DIM_EN = 1 in
Register 0x00. If DIM_EN = 0, the backlight reverts to its
maximum setting.
07445-009
MAX
DIM
BL_EN = 1
DIM_EN = 1 DIM_EN = 0 BL_EN = 0
BACKLIGHT
CURRENT
Figure 18. Backlight Turn On/Dim/Off
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 operation,
users should ensure that the dim setting is programmed to be less
than the maximum setting.
It is also possible to activate the backlight automatically when a
key press is detected. With the row and column pins configured as
a keypad matrix, and the KP_BL_EN bit asserted in Register 0x02,
the internal state machine asserts BL_EN and turns on the back-
light if a key is pressed. See the I/O Expansion Pins (Keypad
Matrix) section for more information on using keypad
functionality.
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.
07445-010
MAX
DIM
BL_EN = 1
BL_EN = 0DIM_EN = 1 DIM_EN = 0
OR
BL_EN = 1
DIM_EN = 1
BACKLIGHT
CURRENT
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 automati-
cally 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.
07445-011
MAX
BL_EN = 1 BL_EN = 0
BACKLIGHT
CURRENT
OFF TIMER
RUNNING
SET BY USER
SET BY INTERNAL STATE MACHINE
Figure 20. Off Timer