ADP5501 datasheet(14/28 Pages) AD

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ADP5501

Rev. 0 | Page 14 of 28

0.2

0.4

0.6

0.8

1.0

UNIT FADE TIME

Figure 30 shows a comparison of fading techniques. Cubic fades

complete faster than linear or square fades for a given fade time

setting. Cubic 1 completes approximately 30% faster, and Cubic 2

completes approximately 10% faster, than an equivalent linear

or square fade time.

With four fade laws and 15 fade time settings, the user can

easily find the right fade experience for an application.

LINEAR

SQUARE

CUBIC 1

CUBIC 2

Figure 30. Fade Law Comparison over a Unit Fade Time

AMBIENT LIGHT SENSING

The ADP5501 can be used in conjunction with an external

photosensor to detect when ambient light conditions drop

below programmable set points. An ADC samples the output of

the external photosensor. The ADC result is fed into two pro-

grammable trip comparators. The ADC has an input range of

0 μA to 1000 μA (typical).

L2_HYS

L2_TRIP

L3_TRIP

L3_HYS

FILTER

SETTINGS

ADC

PHOTO

SENSOR

OUTPUT

L2_EN

L3_EN

L3_

L2_OUT

L3_OUT

L2_

Figure 31. Ambient Light Sensing and Trip Comparators

The Level 2 (office) light sensor comparator, L2_CMPR, is used

to detect when the photosensor output drops below the pro-

grammable L2_TRIP point. If this event occurs, the L2_OUT

status signal is set. L2_CMPR contains programmable hysteresis,

meaning that the photosensor output must rise above L2_TRIP

+ L2_HYS before L2_OUT is cleared. L2_CMPR is enabled in

values of L2_CMPR can be set between 0 μA and 1000 μA in steps

of 4 μA (typical).

L3_CMPR is used to detect when the photosensor output drops

below the programmable L3_TRIP point. If this event occurs,

the L3_OUT status signal is set. L3_CMPR contains program-

mable hysteresis, meaning that the photosensor output must

rise above L3_TRIP + L3_HYS before L3_OUT is cleared.

L3_CMPR is enabled in Register 0x0C via the L3_EN bit. The

L3_TRIP and L3_HYS values of L3_CMPR can be set between

0 μA and 127 μA in steps of 0.5 μA (typical).

L2_TRIP

L2_HYS

L3_TRIP

L3_HYS

100

1000

ADC RANGE (µA)

Figure 32. Comparator Ranges

The L2_CMPR and L3_CMPR comparators can be enabled

independently of each other. The ADC and comparators run

continuously when L2_EN and/or L3_EN is set during auto-

matic backlight adjustment mode. A single conversion takes

80 ms (typical). Filter times of between 80 ms and 10 sec can be

programmed for the comparators before they change state.

It is also possible to use the light sensor comparators in a single-

shot mode. After the single-shot measurement is completed, the

internal state machine clears the FORCE_RD bit in Register 0x0C.

The interrupt flag CMPR_INT is set in Register 0x00 if either of

the L2_OUT or L3_OUT status bits changes state, meaning that

interrupts can be generated if ambient light conditions transition

between any of the programmed trip points. CMPR_INT can

cause the INT pin to be asserted if the CMPR_IEN bit is set in

writing a 1 to it.

AUTOMATIC BACKLIGHT ADJUSTMENT

The ambient light sensor comparators can be used to automat-

ically transition the backlight among its three operating levels. To

enable this mode, the BL_AUTO_ADJ bit is set in Register 0x02.

Once enabled, the internal state machine takes control of the

BL_LVL bits in Register 0x02 and changes them based on the

L2_OUT and L3_OUT status bits in Register 0x0C. The L2_OUT

status bit indicates that ambient light conditions have dropped

below the L2_TRIP point and the backlight should be moved to

its office (L2) level. The L3_OUT status bit indicates that ambient

light conditions have dropped below the L3_TRIP point and the

backlight should be moved to its dark (L3) level. Table 5 shows

the relationship between backlight operation and the ambient

light sensor comparator outputs.

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