TIC12400Q - Thresholds for Rise/Fall time for SPI

Hi Ana,

These parameters are based on 10% - 90%.

Regards,

Jonathan

Hi Jonathan, thank you for the answer! This is not very good news to us, because in our current design we have 50 ns rise/fall times with VIH-VIL 20-80%. With 10-90%, tr anf tf will be above. Interesting the timings between CLK SPI and Data SPI are OK according to the MSDI specification. Do you think such slow rise/fall times will be a problem?

Hi Ana,

What is your bit rate and setup/hold times?  I believe the max rise/fall spec of 30ns are there to ensure the min setup time of 30ns can be achieved.  Setup and Hold times are generally the critical specs that need to be ensured.

Regards,

Jonathan

Hi Jonathan,

Here are the setup and hold times measured by me:

Setup and hold times are measured @30-70% input levels. As you can see, we have very big margins due to the fact that our CLK frequency is 800 kHz.

And here it is a measurement of the rise/fall times with thresholds 30-70%:

This is why I was wondering if the rise and fall times are problem.

Best regards,
Ana

Hi Ana,

I don't believe this is an issue as the data is sampled on the falling edge of SCLK.  From what I can determine, the max rise time of 30ns would only be needed to ensure the minimum SI to SCLK setup/hold times can be achieved.

Regards,

Jonathan

Hi Jonathan,

Thank you! So, it is okay to have bigger rise/fall times as long as we have setup/hold times in spec, meaning we need to have slower frequency -> to have bigger margins?

Best regards,
Ana

Hi Ana,

Yes, that is correct.  You can't have slow rise/fall times with a fast data rate.  You should always verify with testing, but your waveforms look good to me and I wouldn't anticipate any communication issues from them. 

Regards,

Jonathan