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TS5A3359: SD Card not read unless Oscilloscope probe is connected to any of the signals

Daniel Ventura
Prodigy 80 points
Part Number: TS5A3359
Other Parts Discussed in Thread: TS5A3357

Hello

We are testing the TS5A3359 to be able to switch between an SD card and an EMMC memory but unfortunately, we are experiencing some performance issues.

The device works ok on its own, we tested it with a signal generator and all inputs and outputs are working correctly, the problem is when we want to read from the SD card, as the host PCB doesn't seem to be able to detect the SD card connected. 

The weird thing about this is that if we connect an oscilloscope to probe from the N0/N1/N2 side, where the SD card is, the SD card is detected. Needless to say that we only need to connect the oscilloscope probe to 1 signal, it can be any, for the SD card communication to work. Any ideas on why this could be happening?

It will be worth mentioning that the required pull-up resistors for the SDA lines are connected on the COM side of the multiplexor only. Is it required to have pull up resistors in both signal sides of the multiplexor?

See schematics below.

  • 0
    TI__Mastermind 43245 points

    Hi Daniel,

    I think the problem is that it is recommended to have pull-ups on both sides of the multiplexer - as it can cause problems like you are seeing if you don't.  Please try implementing this on both sides and see if this fixes the issue.

    If this doesn't resolve your problem could please re-upload the schematics using the paper clip icon  as copy and pasting images isn't supported by the E2E site at this time, and Unfortunately I can't see the schematic that you have uploaded due to that. 

    Please let me know - and if you are still having problems let me know and I will see what I can do!

    Best,

    Parker Dodson

  • 0 in reply to Parker Dodson
    Prodigy 80 points

    Hi Dodson,

    We have now added the required pull-up resistors on the other side of the mux and the device is operating properly.

    Thanks for your support!
    Regards

    Daniel

  • 0 in reply to Parker Dodson
    Prodigy 80 points

    Hi Dodson,

    Unfortunately, We are still having problems with the Mux.

    I did the hardware change for the pull-up resistors, which worked on the day and stored the boards.
    I put the boards in storage, and a couple of days after, on Wednesday/Thursday, I gave the boards to my embedded team for testing but they did not manage to read the SD card, neither the EMMC. If we connect our previous boards with only the SD card they work perfectly.

    I checked the boards yesterday, Monday, but did not manage to find any issues. I plugged it into a logic analyzer to verify the signals and magically the board worked. I disconnected the logic analyzer and made sure that the boards were working correctly. I tested them 10 times before putting them on the side. 
    Today I try to test the boards again but is not possible to read the SD card again... I know its not an issue on my host board, as they are working 100% of the times with the board that only has the SD card on it.

    Is there anything else that I could try or maybe something that I am doing wrong?
    Please find the schematics and photos of the PCBsSanDiego_1.1.pdf

  • 0 in reply to Daniel Ventura
    TI__Mastermind 43245 points

    Hi Daniel,

    There is nothing that looks wrong with the schematic. 

    Have you tried replacing the units on board and retesting to validate to make sure nothing happened to the IC's themselves?

     It might be because of the high on capacitance of the switch (78pF typical - which is very high for a switch);. This could be causing issues with detection - and capacitance is variable with multiple factors which could explain why there could be some issues. 

    The TS5A3357 has a lower On capacitance (17pF typical) and is pin to pin replacement to the 3359 and (also with higher bandwidth) - and this is most likely going to be better for the application - that being said what is max clock speed going through the device ?

    Please let me know - as I think the bus capacity may be too large due to the switch and a lower on-capacitance switch is needed.

    Best,

    Parker