AM2634: SPI1 Vs SPI3 : Load capacitance

Hi Yassine,

Are you using the SPI3 pins for any other peripheral?

Have you correctly configured the SPI3 pins to operate as SPI using the SysConfig tool?

Regards,

Brennan

Hi Brennan,

SPI3 was working fine before adding the shown filter.

Thanks,
Yassine

Yassine,

What is the part number of the ferrite bead you are using? You may be exceeding the maximum load capacitance.

7427927310 from Wurth 

Ok, ferrite bead part # looks fine.

Do you have scope shots you can share that show the data corruption on SPI3, and the valid data transmission on SPI1?

Hi Brennan,

Please find attached data from SPI1 and SPI3.
During this test we're continuously sending 0x0117 and 0x0542 and reading back using a logic analyzer connected to below point.
SPI3_Data.csvSPI1_Data.csv

Thanks,
Yassine

Yassine,

Thanks for sharing the data. Is the PCB routing for SPI1 and SPI3 identical? Is there any potential for reflections or stubs along the SPI3 traces?

Regards,

Brennan

The routing is not identical, however SPI3 is theoretically better routed than SPI1. There are no stubs on either, but SPI1 is routed near several SMPS circuits. Yet, SPI1 was not affected.
The capacitance limit is 24pF, right ?
is there any difference between SPI1 and SPI3 ?

Regards,
Yassine

Yassine,

Yes, the capacitance limit is 24pF as noted in the data sheet.

There is no difference between the SPI1 and SPI3 instances of the SPI peripheral.

Do you have the same capacitance/filtering on the SPI CLK lines as well? Or just the data traces?

Regards,

Brennan

The same filter is applied on the CLK lines as well - but there's no apparent phase shift that could explain the issue.
and theoretically, the phase shift would be approx 0.3deg at 4MHz.

Also, we didn't see any evidence of an extra clock pulse.

Regards,

Yassine

Yassine,

After discussing this issue with engineers on my team, we have come to the conclusion that we cannot analyze this issue further without oscilloscope shots of the data transmission.

Please provide oscilloscope shots of both SPI1 and SPI3 so I can continue looking into this issue.

Regards,

Brennan