CXA2108AQ
Description of Operation
1. Description
The CXA2108AQ is an LED driver for full color LED displays. The RGB luminance which becomes the video
data is controlled by pulse width modulation (PWM), and the luminance variance of each LED is corrected by
the drive current. The basic PWM clock width can be set in 16 steps from 1× to 16× by the brightness data,
making it possible to adjust the brightness of the entire screen. There are 24 driver outputs, and time division
allows driving of either two or six LEDs per output by adding an external FET or other switch.
The luminance (pulse width), drive current and brightness are set by writing data to the internal memory
according to the memory map. The luminance and drive current can be set independently for each LED.
2. Relationship between the luminance data (PWM data: Dv), brightness data (Db) and the LED emitting duty
The CXA2108AQ adjusts the LED luminance which becomes the video data by changing the LED emitting
time duty through PWM of the luminance data. The luminance consists of luminance data and brightness data.
The luminance data (Dv) has an accuracy of 10 bits (= 1,024 steps: 0 to 1,023) and can be set independently
for each LED. The brightness data (Db) controls the basic PWM clock width with 4 bits (= 16 steps: 1× to 16×),
and is common data for all outputs. The brightness data is normally used when adjusting the brightness of the
entire screen.
Labeling the LED emitting cycle as Ts and the CLK cycle as TCLK , this relationship is given by the following
formula.
Ts = 1,024 × 16 × TCLK
The LED emitting time Tv within this Ts time is:
Tv = Dv × Db × TCLK
Therefore, the emitting duty is:
Tv/Ts × 100 = (Dv × Db)/(1,024 × 16) × 100 [%]
The drive current waveform and the relationship between the luminance data, brightness data and the emitting
duty are shown below.
Current
Tv = Dv × Db × TCLK
IOUT
0
Time
TS = 1,024 × 16 × TCLK
TS
Drive current
Fig. 1. Drive Current Waveform
– 12 –
SONY [ SONY CORPORATION ]
