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About 74HC245 buffering signal for a LED display

Abel Valero
Prodigy 230 points
Other Parts Discussed in Thread: TLC59283

Hi all,

I have a question regarding the typical buffer that it is used to boost the signals coming from a buses when we are working with LED displays.

Normally we have some signals that are buffered before being sent to the LED drivers. Typical ones shared by different LED drivers CLK, OE, LAT.

So, in the datasheet which parameter can I use to know how many devices (LED drivers) can I connect to the same output of the 74HC245?

For example, if I have a CLK at the output of the buffer, how many LED drivers can I feed with this signal?

Thanks and kind regards,

Abel

  • 0
    TI__Intellectual 1820 points

    Hello,

    Basically, we suggest less than 10pcs LED drivers fed by one output of the buffer.

    More drivers fed, will cause the rising/falling edge of output signal(say, here is CLK) to be more slowly, which may cause the effective high level pulse width too narrow. Take tlc59283 as example, see datasheet page 3, the parameter tWH0 require the high level pulse width >10nS, this may can't be satisfied if SCLK rise up too slow(considering 33MHz SCLK condition, 50% duty, the normal high level width is 15nS only).

    The setup time tSU0 and hold time tH0 should also be checked, if the CLK signal delayed by the slowly rising speed.

    Best regards

    Mike

  • 0 in reply to Mike(DC/DC) Wang
    Prodigy 230 points

    Hi Mike,

    now I understand better this parameters that must be regarded to have a good design and performance.

    Thank you very much and kind regards,

    Abel