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WL1837MOD: TXS0108 SDIO interface signal integrity issue

Part Number: WL1837MOD
Other Parts Discussed in Thread: WL1837, TXB0108

We are using WL1837 MOD in our design for WiFi interface which is interfaced to a host SDIO bus with 3V3 IO logic level. We are using TXS0108EPWR for the translation between 3V3 logic level and 1V8 logic level. But we are observing signal integrity issues on the SDIO signals. The waveform are distorted and there are overshoots and undershoots.

As an alternate we have tried the translator TXB0108 in place of TXS0108. But the SDIO interface is not functional at all when TXB0108 is being used. Is there any known fix for this issue? 

  • Hi,

    I sent it to a concerned engineer. They will get back to you ASAP. Please bare with us.

    Thanks,

    PM

  • Hi Thomas,

    Did you design your board using the WL18xx checklist?

    If not, can you verify the following guidelines are followed on your design:

    1. Route SDIO signal traces (CLK, CMD, D0, D1, D2, and D3) in parallel to each other and as short as possible (less than 12 cm)
    2. The SDIO interface lines aer matched in length, 6 – 7 mil width trace with separation between the lines of 2x width. Avoid adding many vias on the routing
    3. enough space between traces (greater than 1.5 times the trace width or ground) to ensure signal quality, especially for the SDIO_CLK trace
    4. these traces kept away from the other digital or analog signal traces. TI recommends adding ground shielding around these buses
    5. Digital clock signals (SDIO clock, PCM clock, and so on) are a source of noise. Keep the traces of these signals as short as possible. Whenever possible, maintain a clearance around these signals

    Thanks,

    Alexis

  • Thanks for the reply, can you please advice on the second question what could be the reason TXB0108 is making the interface to NOT work functionally? 

    We have observed similar SI issue on the BT UART lines also where TXS0108 was used and there we could resolve the SI issue by replacing the TXS0108 with 74LVC4T245. That is the reason we are trying alternate translator TXB0108 in this case also for SDIO and found the interface is not functional when TXB0108 is used.

  • Hi Thomas,

    Have you read through the Level Shifting WL18xx/WL18xxMOD/WL18xxQ I/Os App note? 

    Thanks,

    Alexis

  • Hi Alexis,

    Thanks for the response.

    Yes, we have used the translator TXS0108 in our design as per the guidelines in said App Note. But we are facing SI issues with while using TXS0108. That is the reason we want to try the translator TXB0108 which is similar to TXS0108, but doesn't support external pull ups. But the WLAN SDIO interface is not functional when using TXB0108. Now our question is 'What could be the reason for the WLAN SDIO interface to be non-functional when TXB0108 is in use? Is this already observed behavior and is there any fix available? 

    Regards,

    Thomas CN

  • Hi Thomas,

    I recommend going back to using the TXS0108 as it is the part TI recommends. Again, the issue may be layout related so can you please verify that you are following the guidelines i mentioned previously?

    Thanks,

    Alexis

  • Hi Thomas,


    I haven’t heard back from you, hence this issue is being closed. If you wish to continue the discussion, please post a reply with an update below (or create a new thread).

    Thanks,

    Alexis

  • Hi Alexis,

    Thanks for the support. However the question 'Why TXB0108 is not working when used in place of TXS0108?' was not answered yet.

    Regards,

    Thomas CN

  • Hi Thomas, 

    The TXS0108 is optimized for translation applications (like card interfaces) that require the system to start out in a low-speed open-drain mode and then switch to a higher speed push-pull mode. The TXB0108 does not support open-drain applications. 

    Thanks,

    Alexis