AAT3129
High Efficiency 1X/1.5X/2X Charge Pump
for RGB Color LED Applications
Color Registers R, G, and B
Intensity Register T
The individual color brightness is set using the
three R, G, and B registers. The data register con-
tents determine the on-time for each color channel
during a PWM cycle. The first level is 0, or off, and
is set with a single EN/SET rising edge. This setting
eliminates a given color from the spectrum. The
remaining 15 levels progressively increase the
brightness for a particular color by increasing that
channel’s on-time. Using the red channel as an
example, the resulting on-time is
The overall intensity level is set by the T register.
Once a particular mixing of colors is set to produce
the desired color, the overall intensity can be
adjusted while keeping constant the ratio of colors
to one another. The brightest level is set by pro-
gramming the T register with 1 edge. Programming
the T register with 16 edges produces the dimmest
setting. The T register adjusts the overall intensity
by controlling the PWM off-time. Under the
dimmest setting, the off-time is the longest. The off-
time that results from the data in the T register is
on-time = (R - 1) · 128µs
off-time = (T - 1) · 512µs
where R is the data setting (from 1 to 16). The
same applies to G and B.
Diode Current Timing
(R - 1) · 128µs
128µs
ISRC
(T - 1) · 512µs
ISRC
Red
(G - 1) · 128µs
ISRC
128µs
Green
(B - 1) · 128µs
128µs
ISRC
Blue
By using synchronized updating, discrete changes
in color can be achieved. Synchronized updating
allows the intensity for all three colors to be updat-
ed simultaneously. All three color registers can be
loaded with new data prior to the update. Then,
upon loading the T register, all three colors will
change to their new states together. This allows a
user to transition from one mixed color to another
without having to traverse intermediate colors.
Under immediate updating color changes can only
be achieved serially, or one color at a time.
Mode Register M
The mode register determines the method of
update for the R, G, and B channels. When the
mode register is set to 1, the addressed color
updates immediately. When the mode register is
set to 2, the colors will update when the T register
is written (synchronized updating).
Under immediate updating, an addressed channel
will update as soon as new data has latched for it.
Under synchronized updating, the channels that
have been assigned new data will not update until
data for the T register latches.
3129.2005.11.1.3
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