ADP8863ACPZ-R7 datasheet(17/48 Pages) AD

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ADP8863

Rev. 0 | Page 17 of 48

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 36. 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 = 0

DIM_EN = 1

BACKLIGHT

CURRENT

DIM TIMER

RUNNING

OFF TIMER

RUNNING

SET BY USER

SET BY INTERNAL STATE MACHINE

Figure 37. 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 = 0

BL_EN = 1

(REASSERTED)

FADE-IN

OVERRIDDEN

FADE-OUT

OVERRIDDEN

Figure 38. 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 39). The currents for the different lighting modes

are defined in the BLMXx and BLDMx registers (see the

Backlight Operating Levels Section).

BRIGHTNESS

DARK

OFFICE

DAYLIGHT

0 LUX

L2_OUT = 1

L3_OUT = 1

L2_OUT = 1

L3_OUT = 0

L2_OUT = 0

L3_OUT = 0

Figure 39. 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).

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