Datasheet

ADP8863
Rev. A | Page 15 of 52
1.00
The Cubic 10 and Cubic 11 laws also use the square law LED
currents derived from Equation 3; however, the time between
each step is varied to produce a steeper slope at higher currents
and a shallower slope at lower currents (see Figure 30).
30
0
5
10
15
20
25
00.750.500.25
CURRENT (mA)
UNIT FADE TIME
LINEAR
SQUARE
CUBIC 11
CUBIC 10
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Figure 30. Comparison of the Dimming Transfers Laws
Each LED can be enabled independently and has its own
current level, but all LEDs share the same fade in rates, fade out
rates, and fade law.
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) in conjunction with the off timer of
each ISC (SC1OFF, SC2OFF, SC3OFF, SC4OFF, SC5OFF, SC6OFF,
and SC7OFF) allows the LED current sinks to be configured in
various blinking modes. The on timer can be set to one of four
different settings: 0.2 sec, 0.6 sec, 0.8 sec, or 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.
Program all fade, on, and off timers before enabling any of the
LED current sinks. If ISCx is on during a blink cycle and
SCx_EN is cleared, the LED turns off (or fades to off if fade out
is enabled). If ISCx is off during a blink cycle and SCx_EN is
cleared, it stays off.
MAX
SCx_EN
FADE-IN FADE-OUT FADE-IN FADE-OUT
ON TIME ON TIME
SET BY USER
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ISCx
OFF
TIME
OFF
TIME
Figure 31. Independent Sink Blink Mode with Fading
RGB COLOR GENERATION
The ADP8863 is easily programmed to generate any color with
an RGB LED. To configure this feature, connect each LED in a
standard RGB diode to a separate driver on the ADP8863.
Because each channel can be programmed for a different
current level, setting the currents for all three LEDs generates
the desired color. To set the current levels, use a simple RGB
color selector (see Figure 32).
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Figure 32. Standard RGB Color Generator
The example in Figure 32 shows a color of green, which is gener-
ated with a red content of 18 (out of 255), a green content of
190, and a blue content of 96. All numbers are out of a maximum
of 255. Thus, the percentage of red is 7.1%, the percentage of
green is 74.5%, and the percentage of blue is 37.6%. To generate
the color with the ADP8863, scale this value to each of the current
drivers.
AUTOMATED RGB COLOR FADES
The ADP8863 is easily programmed to cycle through RGB
generated colors. This can be either a repeating or a random
pattern of one color fading into the other. To execute this cycle
autonomously, set up the RGB LEDs as described in the RGB
Color Generation section and program the on, off, fading times,
and current intensities. Adjusting the fading time in particular
can create any pattern from a fast, striking effect to a soothing
slow color change.