ADP8860ACBZ-R7 datasheet(20/52 Pages) AD

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ADP8860

Rev. 0 | Page 20 of 52

contains programmable hysteresis, meaning that the photo-

sensor output must rise above L3_TRP + L3_HYS before

L3_OUT clears. L3_CMPR is enabled via the L3_EN bit. The

L3_TRP and L3_HYS values of L3_CMPR can be set between

0 μA and 137.7 μA (typical) in steps of 0.54 μA (typical).

L2_TRP

L2_HYS

L3_TRP

L3_HYS

100

1000

ADC RANGE (µA)

Figure 40. Comparator Ranges

Note that the full-scale value of the L2_TRP and L2_HYS

registers is 250 (decimal). Therefore, if the value of L2_TRP +

L2_HYS exceeds 250, the comparator output is unable to

deassert. For example, if L2_TRP is set at 204 (80% of the full-

scale value, or approximately 0.80 × 1080 μA = 864 μA), then

L2_HYS must be set at less than 46 (250 − 204 = 46). If it is not,

then the L2_HYS + L2_TRP exceeds 250 and the L2_CMPR

comparator is never allowed to go low.

When both phototransistors are enabled and programmed

in automatic mode (through Bit L3_EN and Bit L2_EN in

to determine which of the comparator outputs to use, selecting

Bit SEL_AB in Register 0x04 for automatic light sensing

transitions. For example, the user’s software may select the

comparator of the phototransistor exposed to higher light

intensity to control the transition between the programmed

backlight intensity levels.

The L2_CMPR and L3_CMPR comparators can be enabled

independently of each other, or can operate simultaneously. A

single conversion from each ADC takes 80 ms (typical). When

CMP_AUTOEN is set for automatic backlight adjustment (see

the Automatic Backlight Adjustment section), the ADC and

comparators run continuously. If the backlight is disabled and

at least one independent sink is enabled, it is possible to use the

light sensor comparators in a single shot mode. A single shot

read of the photocomparators is performed by setting the

FORCE_RD bit. After the single shot measurement is completed,

the internal state machine clears the FORCE_RD bit.

The interrupt flags (CMP_INT and CMP_INT2) can be used to

notify the system when either L2 or L3 changes state. Refer to

the Interrupts section for more information.

AUTOMATIC BACKLIGHT ADJUSTMENT

The ambient light sensor comparators can automatically

transition the backlight between one of its three operating

levels. To enable this mode, set the CMP_AUTOEN bit in

When enabled, the internal state machine takes control of the

BLV bits and changes them based on the L2_OUT and L3_OUT

status bits. When L2_OUT is set high, it indicates that the

ambient light conditions have dropped below the L2_TRP point

and the backlight should move to its office (L2) level. When

L3_OUT is set high, it indicates that ambient light conditions

have dropped below the L3_TRP point and the backlight should

move to its dark (L3) level. Table 6 shows the relationship

between backlight operation and the ambient light sensor

comparator outputs.

The L3_OUT status bit has greater priority; therefore, the

backlight operates at L3 (dark) even if L2_OUT is set.

Filter times of between 80 ms and 10 sec can be programmed

for the comparators (Register 0x1B and Register 0x1C) before

they change state.

Table 6. Comparator Output Truth Table

CMP_AUTOEN

L3_OUT

L2_OUT

Backlight Operation

BLV can be manually set

by the user

BLV = 00, backlight

operates at L1 (daylight)

BLV = 01, backlight

operates at L2 (office)

BLV = 10, backlight

operates at L3 (dark)

1 X is the don’t care bit.

INDEPENDENT SINK CONTROL

Each of the seven LEDs can be configured (in Register 0x05) to

operate as either part of the backlight or to operate as an indepen-

dent sink current (ISC). Each ISC can be enabled independently

and has its own current level. All ISCs share the same fade in

rates, fade out rates, and fade law.

The ISCs have additional timers to facilitate blinking functions.

A shared on timer (SCON) used in conjunction with the off

timers of each ISC (SC1OFF, SC2OFF, SC3OFF, SC4OFF,

SC5OFF, SC6OFF, and SC7OFF) allow the LED current sinks to

be configured in various blinking modes. The on timer can be

set to four different settings: 0.2 sec, 0.6 sec, 0.8 sec, and 1.2 sec.

The off timers have four different settings: disabled, 0.6 sec,

1.2 sec, and 1.8 sec. Blink mode is activated by setting the off

timers to any setting other than disabled.

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