TLC6989 datasheet(47/72 Pages) TI1

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8.2.2 Detailed Design Procedure

At first the designer needs to determine the required CCSI data rate for the application. The minimum CCSI data

rate is coming from the brightness information that needs to be transmitted to all the LED drivers within one

frame period. The data sheet of the chosen LED driver gives more details about the minimum required CCSI

data rate. In this application example the frame period is 33.33ms. There are 6 devices in the daisy chain (3

groups of 2 stackable mode) with 30 scan lines. When a data transmission efficiency of 70% is assumed (since

there could be some idle time between transmitted CCSI commands), the minimum required CCSI data rate is

7.04Mbit/s. Therefore, the CCSI_DATA_RATE in register CCSICTRL is set to 8Mbit/s.

The SPI frequency is gerenally set to be in the similar range as the CCSI data rate. Therefore, in this application

example the SPI frequency is set to 8MHz. The next step is to determine the TXFFLVL. TI recommends to

set TXFFLVL larger than the maximum number of words that are forwarded for one CCSI command. The

maximum number of words happen for a data write command with non-broadcast, e.g. write SRAM command.

For this command, the number of words are equal to 3 times the number of cascaded devices plus one head

byte. In this application example, the maximum number of words is 19 (3 x 6 + 1) words. Note that when SPI

command FWD_WR_CRC is used, the TXFFLVL is ignored, and the forwarding only starts when the CRC word

is correct. In addition, during the forwarding by the CCSI controller, the next SPI forward command can already

be transmitted by the SPI controller because of the CCSI command queue in the TLC6989.

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TLC6989

SLVSHF5 – NOVEMBER 2024

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TLC6989 Datasheet(PDF) 47 Page - Texas Instruments