Datasheet

ADP8863
Rev. A | Page 17 of 52
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
08392-041
Figure 37. Off Timer
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, and BL_EN asserted, the backlight turns
on to its maximum setting, and 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 = 0DIM_EN = 1
BACKLIGHT
CURRENT
DIM TIMER
RUNNING
OFF TIMER
RUNNING
SET BY USER
SET BY INTERNAL STATE MACHINE
08392-042
Figure 38. Dim and Off Timers Used Together
FADE OVERRIDE
A fade override feature (FOVR in Register CFGR (0x04)) enables
the host to override the preprogrammed fade in or fade out
settings. If FOVR is set and the backlight is enabled in the
middle of a fade out process, the backlight instantly (within
approximately 100 ms) returns to its maximum setting. Alter-
natively, if the backlight is fading in, reasserting BL_EN overrides
the programmed fade in time, and the backlight instantly goes
to its final fade value. This is useful for situations in which a key
is pressed during a fade sequence. However, if FOVR is cleared
and the backlight is enabled in the middle of a fade process, the
backlight gradually brightens from where it was interrupted (it
does not go down to 0 and then comes back on).
MAX
BACKLIGHT
CURRENT
BL_EN = 1 BL_EN = 0
BL_EN = 1
BL_EN = 0BL_EN = 1
(REASSERTED)
FADE-IN
OVERRIDDEN
FADE-OUT
OVERRIDDEN
08392-043
Figure 39. Fade Override Function (FOVR Is High)
AMBIENT LIGHT SENSING
The ADP8863 integrates two ambient light sensing compara-
tors. One of the ambient light sensing comparator pins
(CMP_IN) is always available. The second pin (D6) has an
ambient light sensor comparator (CMP_IN2) that can be
activated rather than connecting an LED to D6. Activating
the CMP_IN2 function of the pin is accomplished through the
CMP2_SEL bit in Register CFGR. Therefore, when the CMP2_
SEL bit is set to 0, Pin D6 is programmed as a current sink.
When the CMP2_SEL bit is set to 1, Pin D6 becomes the input
for a second phototransistor.
These comparators have two programmable trip points (L2 and
L3) that select one of the three backlight operation modes
(daylight, office, and dark) based on the ambient lighting
conditions.
The L3 comparator controls the dark-to-office mode transition.
The L2 comparator controls the office-to-daylight transition
(see Figure 40). The currents for the different lighting modes
are defined in the BLMXx and BLDMx registers (see the
Backlight Operating Levels Section).
BRIGHTNESS
L3 L2
DARK OFFICE DAYLIGHT
0 LUX
0A
L2_OUT = 1
L3_OUT = 1
L2_OUT = 1
L3_OUT = 0
L2_OUT = 0
L3_OUT = 0
08392-044
Figure 40. Light Sensor Modes Based on the Detected Ambient Light Level
Each light sensor comparator uses an external capacitor together
with an internal reference current source to form an analog-to-
digital converter (ADC) that samples the output of the external
photosensor. The ADC result is fed into two programmable trip
comparators. The ADC has an input range of 0 µA to 1080 µA
(typical).