Datasheet

ADP5520
Rev. A | Page 14 of 40
ADVANCED FADING (CUBIC 1 AND CUBIC 2)
Two additional advanced techniques are available for fading the
backlight brightness levels, Cubic 1 (BL_LAW = 10) and Cubic 2
(BL_LAW = 11). Referring to the backlight brightness control
block diagram shown in Figure 14, linear and square fading is
implemented by ramping the 128 linear/square algorithm codes
at a fixed frequency over the duration of a given fade-in/fade-
out time.
Cubic fading is implemented by reusing the square algorithm
codes, but by ramping them with a clock source whose frequency
output increases as the sink current code increases (see Figure 29).
Cubic 1 and Cubic 2 differ by having separate frequency vs.
code characteristics.
DARK_MAX
DAYLIGHT_MAX
DAYLIGHT_DIM
OFFICE_MAX
OFFICE_DIM
DARK_DIM
MUX
BST
BL_VALUE
COUNTERS
AND
CONTROL
LOGIC
BL_DIMT
BL_FI
BL_FO
BL_OFFT
BL_EN
DIM_EN
BL_LAW
CLOCK
GENERATOR
BL_LVL
07445-020
BL_SNK
Figure 29. Backlight Brightness Control (Cubic)
Figure 30 shows a comparison of fade law 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, users have tremend-
ous flexibility to find the right fade experience for their application.
07445-021
30
25
20
15
10
5
0
0 0.2 0.4 0.6 0.8 1.0
UNIT FADE TIME
BACKLIGHT CURRENT (mA)
LINEAR
SQUARE
CUBIC 1
CUBIC 2
Figure 30. Fade Law Comparison Over a Unit Fade Time
AMBIENT LIGHT SENSING
The ADP5520 can be used in conjunction with an external
photosensor to detect when ambient light conditions have
dropped below programmable set points. An ADC 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 1000 µA (typical).
07445-022
L2_HYS
L2_TRIP
L3_TRIP
L3_HYS
FILTER
SETTINGS
ADC
PHOTO
SENSOR
OUTPUT
L2_EN
L3_EN
L2_OUT
L3_OUT
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 has dropped below the
programmable 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 Register 0x0C via the L2_EN bit. The L2_TRIP and
L2_HYS values of L2_CMPR can be set between 0 µA and 1000 µA
(typical) in steps of 4 µA (typical).
L3_CMPR is used to detect when the photosensor output
has dropped below the programmable L3_TRIP point. If this
event occurs, the L3_OUT status signal is set. L3_CMPR contains
programmable 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 (typical) in steps of 0.5 µA (typical).
L2_TRIP
L2_HYS
L3_TRIP
L3_HYS
1 10 100 1000
ADC RANGE (µA)
07445-023
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 are set, during
automatic backlight adjustment mode. A single conversion