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ISOUSB211: ISOUSB211 troubleshooting

Anwar Ali Vali Mohamed
Prodigy 90 points
Part Number: ISOUSB211
Other Parts Discussed in Thread: TPS767

Dear TI,

Need some help in troubleshooting my own ISOUSB211 board used for computer-based audio playback.

I pretty much copied TI's EVM design with all external LDOs for both sides.  The only thing I changed was I omitted the ferrite beads since I don't use the DC-DC converter.  A separate low-noise LPSU is used to power the peripheral side.  In my application, the peripheral is digital to analog converter (DAC) for audio with USB interface.

The issue I have was after PC reboot, the connection to DAC is lost.  No such issue when EVM was used.

What is wrong with my circuit?

Thank you TI.

Regards,

Anwar

  • 0
    TI__Guru 54815 points

    Hi Anwar,

    Thanks for reaching out and sorry to hear about the issue.

    Please allow me to review the issue internally and come back to you tomorrow with our inputs on possible causes and suggestions to fix it. Thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 90 points

    Hi Koteshwar,

    Pictures of the isolation chips which I hope can help TI find the possible causes.

    This is the isolation chip on the EVM board (mfg July 2021).

    This is the isolation chip I purchased (mfg Nov 2021).  Picture was taken during hand soldering.

    Thank you.

    Regards,

    Anwar

  • 0 in reply to Anwar Ali Vali Mohamed
    TI__Guru 54815 points

    Hi Anwar,

    Thanks for sharing device images.

    I have looked at the LTC codes of these devices and I do not see any concern with them.
    I also didn't see any obvious issues in the schematic either. Did you also follow the PCB layout guidelines from the ISOUSB datasheet?


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 90 points

    Hi Koteshwar,

    For USB data lines, I used impedance calculator provided by the PCB manufacturer.

    Everything works fine except during PC reboot it lost the USB DAC connection. High-resolution audio transmission works flawless, up to 384k PCM and DSD 256.

    Thanks,
    Anwar

  • 0 in reply to Anwar Ali Vali Mohamed
    TI__Guru 54815 points

    Hi Anward,

    Thanks for further inputs.

    To try debug the issue, can you please configure the EVM the same way you have powered your PCB? That is, disable the SN6505 and the LDO at the transformer output, so that the board can be powered externally? Let me know if you are able to reproduce the issue on the EVM. Thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 90 points

    Yes, I tested EVM in that configuration before I developed my own PCB.  Please see the picture below and note J15 position which disables U3 LDO.  Both L1 and L2 removed and replaced with solder jumpers.  The 5V connector at the input side is not used.  The 5V connector at the peripheral side wired to audio-grade LPSU.  No issues at all as it works perfectly.  After music server reboot, connection to USB Audio DAC is not lost.

  • +1 in reply to Anwar Ali Vali Mohamed
    TI__Guru 54815 points

    Hi Anwar,

    Thanks for further inputs. I have following debug suggestions to try,

    1. Could you please add a 10uF capacitor in parallel with C1 (US VBUS) and 10uF in parallel with C5 (DS VBUS)?
      1. I see this decap is one difference between your PCB and the EVM.
      2. If 10uF does not work, try 22uF.
      3. Eventually, USB standard needs 120uF cap on the VBUS on the Downstream ports that can face dynamic attach. This is something to be taken care later in the design if required.
    2. If 1 does not work, then bypass the U1 LDO and connect US VBUS to device VBUS1 pins so that the internal LDO of ISOUSB211 generates the Please keep a 0.1uF decoupling cap on the V3P3V1 pin.
      1. On the EVM, in the default configuration, the US VBUS is connected directly to the VBUS1 pin of ISOUSB211, with 3.3V generated by the internal LDO.
    3. If 1 and 2 don’t work, then could you please swap out the IC from the EVM into your design, and the device from your design on to the EVM – to narrow down if this is a device or design issue.

    Please do help test the above suggestions and let us know your observations, thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 90 points

    Hi Koteshwar, you are too good!

    I added 10uF cap (the same one used as TPS767 output capacitors) in parallel with the Vishay MKP1837 0.1uF (the black cube caps). USB Audio DAC connection is good after music server reboot.  I tried rebooting multiple times, no more issues.

    I really want to thank you for helping me resolve this issue.  You are superb!

    The timing of this problem resolution is perfect.  I am in the process of making the final PCB.  I made the ISOUSB211 footprint corrections myself since I cannot wait any longer.

    Regards,
    Anwar

  • 0 in reply to Anwar Ali Vali Mohamed
    TI__Guru 54815 points

    Hi Anwar,

    Glad to hear that the issue is resolved and thanks for trying out the suggestions and sharing the update.

    I would also like to let you know that the footprint available online is already updated to 0.65mm pitch and matches the datasheet, you can use this updated footprint for your design. Thanks.


    Regards,
    Koteshwar Rao