ADP8860ACPZ-R7 datasheet(19/52 Pages) AD

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ADP8860

Rev. 0 | Page 19 of 52

MAX

DIM

BACKLIGHT

CURRENT

BL_EN = 1

BL_EN = 0

DIM_EN = 1

DIM TIMER

RUNNING

OFF TIMER

RUNNING

SET BY USER

SET BY INTERNAL STATE MACHINE

Figure 36. 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 where 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 come back on).

MAX

BACKLIGHT

CURRENT

FADE-IN

OVER-RIDDEN

FADE-OUT

OVER-RIDDEN

BL_EN = 1

BL_EN = 0 BL_EN = 1 BL_EN = 0

BL_EN = 1

(RE-ASSERTED)

Figure 37. Fade Override Function (FOVR is High)

AMBIENT LIGHT SENSING

The ADP8860 integrates two ambient light sensing comparators.

One of the ambient light sensing comparator pins (CMP_IN)

is always available. The second pin (D6/CMP_IN2) can be

activated rather than connecting an LED to D6. Activating

the CMP_IN2 function of the pin is accomplished through

Bit CMP2_SEL in Register CFGR. Therefore, when Bit CMP2_SEL

is set to 0, Pin D6/CMP_IN2 is programmed as a current sink.

When Bit CMP2_SEL is set to 1, Pin D6/CMP_IN2 becomes

the input for a second phototransistor.

These comparators have two programmable trip points (L2 and

L3) that select among three of the 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 38). 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 38. 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).

L2_HYS

L2_TRIP

L3_TRIP

L3_HYS

FILTER

SETTINGS

ADC

PHOTO

SENSOR

OUTPUT

L2_EN

L3_EN

L2_OUT

L3_OUT

Figure 39. Ambient Light Sensing and Trip Comparators

The L2_CMPR detects when the photosensor output has dropped

below the programmable L2_TRP point (Register 0x1D). If this

event occurs, then the L2_OUT status signal is set. L2_CMPR

contains programmable hysteresis, meaning that the photo-

sensor output must rise above L2_TRP + L2_HYS before

L2_OUT clears. L2_CMPR is enabled via the L2_EN bit. The

L2_TRP and L2_HYS values of L2_CMPR can be set between

0 μA and 1080 μA (typical) in steps of 4.3 μA (typical).

The L3_CMPR detects when the photosensor output has

dropped below the programmable L3_TRP point (Register 0x1F).

If this event occurs, the L3_OUT status signal is set. L3_CMPR

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