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As shown in
Figure
Section F, and each section is the minimum unit of the whole LED display board. In each section, 30
MOSFETs control the power supply for the 30-line LED anode; 15 TLC6946 devices are cascaded to drive
80 RGB LEDs (240 LEDs).
SYSTEM STRUCTURE
TLC6946 devices per LED display board
P-channel MOSFETs per LED display
board
4.1.1.2
SCLK and GCLK Frequency
SCLK is the serial-data shift-in clock signal; and GCLK is the PWM-control reference-clock signal.
Equation 4
shows the minimum frequency requirement for GCLK and SCLK.
m n f
f
GCLK
1 t
LSW
f
N n 16 16 f
u u
SCLK
where
•
f
is the minimum GCLK frequency for single-edge operating mode
GCLK
•
f
is the minimum SCLK frequency
SCLK
•
f
is the visual refresh rate of the entire cascading series
VR
•
f
is the frame rate per second
FPS
•
m is the number of GCLKs for each sub-period, determined by the PWM mode selected
•
n is the number of scan lines
•
N is the number of cascaded TLC6946 devices
•
t
is the line switching time
LSW
Table 4-3
shows the SCLK and GCLK minimum frequency requirement.
DESIGN PARAMETER
Number of GCLKs for each sub-period (m)
Number of scan lines (n)
Number of cascaded TLC6946 devices (N)
Line switching time (t
Dual edge f
4.1.1.3
Channel Current and Brightness Control
Select the reference current-setting resistor R
Section
2.3.1.2). Select the BC data for the best white balance of the red, green, and blue LEDs (see
Section
2.3.1.1).
There are two methods to set the different-color LED currents:
1. Use the same resistor for the red, green, and blue LEDs, and use the BC register to set a different
current for each color.
2. Use different resistors for the red, green, and blue LEDs, and use the BC register to fine-tune the
current for each color.
SLVUBF4A – February 2018 – Revised June 2019
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TI Information — Selective Disclosure
4-1, each LED display board can be divided into six sections, Section A through
Table 4-2. TLC6946 System Structure
u u
VR
n f
u u
VR
u
u
FPS
Table 4-3. SCLK and GCLK Frequency
)
LSW
f
GCLK
GCLK,B
f
SCLK
Copyright © 2018–2019, Texas Instruments Incorporated
EXAMPLE VALUE
90
180
EXAMPLE VALUE
310 (8+8 mode, default register setup)
to set the maximum current of each color LED (see
IREF
TLC6946 Design Example
30
15
1.5 µs
43.2 MHz
21.6 MHz
6.9 MHz
Device Operation Examples
(4)
39
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