AM35x SDIO at low temperature

Hi,

Are you sure that the SD card is operative at these temperatures?

Hi Biser,

Thank you for the quick response.
Yes the SD card is operative at these temperatures, actually different
kinds/makers of SD cards has been tried and the result was same.

Looking into the Oscilloscope waveforms,we believe the AM35xx's SDIO line (CMD line)
output is going High-Impedance during this issue.
If possible could you please let us know if there is any possiblilty or any
situation that could cause AM35xx's CMD line output to High-Impedance?
or is there any possiblity that AUTO CMD12 could cause High-Impedance?
(I could send you the waveform through offline)

According to our understanding this issue occurs only with the Auto CMD12,
if possible we would like to know at what condition AM35xx SDIO controller
would issue the Auto CMD12.

Best Regards
Kummi

The controller itself does not issue commands. This is done by software. Do you have external pullups on the SDIO lines?

Hi Biser,

Yes, external pullups are used on the SDIO Lines.

Best Regards
Kummi

Hi Biser,

With regards to this issue, please let me know if there is any details
about the below general question about SDIO command CMD12.

We would like to know in general that Auto CMD12 is used in most of the applications?
and what are the things to be considered if we use software CMD12 instead of Hardware Auto CMD12.

Currently the solution could be using software CMD12 instead of Auto CMD12, but we are searching for
the reason to explain to the customer why this issue occurs(High-Impedance output at low temperature).

Best Regards
Kummi

This issue has been forwarded to the factory team. They should respond directly here.

Kummi, i have a few questions:

-You mentioned that this issue started occurring when they removed a Zener diode on the CMD signal and replaced it with 100pF capacitor.  And the issue still occurs even with the capacitor removed.  Did this issue occur at low temps with Zener diode installed?  DId they ever test at low temps with Zener diode installed?

-As a test, can they try running the interface at a slower speed to see if the issue still occurs?

-What was the configuration of the hardware with the scope shots you sent?  Was the capacitor installed, and what value?  The only thing that changed  between error and normal scope shots  was the temperature?  

Regards,

James

Hi James,

Thank you very much for the reply.

1.With regards to the zener diode, it was removed bcos they had issue with the SD Card timings,
   it was replaced by a capacitor(56pF).And the issue occurs even if there is a capacitor or removed.
   They have tested at low temps with zener diode and this issue might have occurred even with the
   Zener Diode but may not have came out as an error like this time.

2.Will check if they could do the test at slower speed.

3.There is no hardware difference between the scopes, one is the scope with the error and the other is
   normal.This issue occurs only during low temperature. 0 to 10deg and 0 to -10deg.
   We can say the only difference is the temperature.
   As mentioned above the capacitor is 56pF and it occurs when capacitor is installed or removed.

Best Regards
Kummi

Hi James,

With regards to "running the interface at a slower speed",
we tried with the slower clock(400Khz) and there was no issue as such.
(clock speed when this issue occur is 24Mhz)

Best Regards
Kummi.

Kummi, can you please try another experiment by removing all capacitance on all MMC signals?  External capacitance will negatively affect interface timing.  

Also, what was the h/w configuration with the slower speed that was successful?  Did they have capacitance on all signals?  What value?

Regards,

James 

Hi James,

Yes, they have tried by removing all the capacitance on all MMC signals
and the issue still occurs.

And the h/w configuration with the slower speed was that they had the
capacitance on CMD line(56pF) and CLK(47pF)....same as the schematics which we
have sent you before.

Best Regards
Kummi

Hi Kummi, we have one more experiment.

-with all of the capacitance removed from all signals, replace the 0ohm series termination resistor on MMC_CLK with a 22ohm resistor.

By the way, where is the MMC_CLK series resistor physically located. Is it near the processor, or near the card? Ideally, it needs to be as close to the processor as possible.

Regards,
James

Hi James,

They have tried with all of the capacitance removed from all signals and replaced
the 0ohm series termination resistor on MMC_CLK with a available 30ohm resistor
and the result was same, the issue occurs...
And the MMC_CLK series resistor is close to the processor.

With regards to the slower speed test, there was no capacitor installed.

Actually they have already done number of testing with regards to the external elements like
resistor or capacitors and the conclusion is that there seems to be no effect as
such from the external capacitance or any other elements.

As mentioned previously this problem occurs even without connecting a SD card,
so we believe this could be a hardware issue of AM3505 SDIO controller.

Could you please let us know if there is any possibilty that AM3505 SDIO's
CMD line could go High Impedance? Meanwhile can we assume that there is no problem
in the customer's schematics?

Best Regards
Kummi

Any comments. Can we assume the schematics is all right?