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ISOUSB211: The output fails when the USB disk is inserted.

user5883945
Expert 1566 points
Part Number: ISOUSB211

Dears:

    We use ISOUSB211 as usb isolation relay. If the USB flash drive is not inserted, the output D+ D- can restore the MCU signal DM DP.

    After the USB flash drive is inserted, the output fails. DP(DD+) D+(UD+) become to high level; DM(DD-) D-(UD-) become low leval.

    The waveform from DP  DM  D+ D- as attachment, 

    pls give some advice, thanks!

    test report.docx

  • 0
    TI__Guru 54495 points

    Hi,

    Thanks for reaching out and for sharing the waveform along with schematic.

    I see that customer is using internal LDOs for both sides to generate the 1.8V output. This does dissipate quite some power especially in the HS mode which happens when a HS device is connected. For debugging purpose, could you please ask customer to repeat the test by connecting power externally (especially for 1.8V pins) and avoid using internal LDOs?

    This means connecting 1.8V external supply to V1P8V1 & VCC1 pins and V1P8V2 & VCC2 pins. Please do request this test and let us know customer observations, thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Expert 1566 points

    Dear Koteshwar:

        The test result as blow

    USB TEST RECORD 2022.10.25.docx

  • 0 in reply to user5883945
    TI__Guru 54495 points

    Hi,

    Thanks for the updated report.

    1. From your schematic, I am assuming the USB flash drive is connected to the connector J14. The USB standard requires that a 120µF capacitor is placed on the VBUS pin of the USB port that connects to peripherals (like USB flash drive) to support the in-rush current from the peripherals. I do not see your schematic having this, could you please add this capacitor? Please refer to section 10.1.1 and figure 10-1 of the datasheet. I am copying figure below for your reference.
    2. I am not sure about the current requirement of the USB flash drive that you are trying to connect, please ensure that the 5V rail "USB_5V" supports that current in addition to providing the current to ISOUSB211.
    3. The decoupling capacitors on all supply pins on VBUS2 side look good and follow datasheet recommendations. The power supply generating VDD_3V3 might require a higher decoupling capacitor on the supply pins, please ensure sufficient decoupling capacitors is placed on this rail accordingly.

    Please do consider the suggestions provided above and let us know if this addresses the issue you are facing, thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    TI__Guru 54495 points

    Hi,

    Checking in to see if the suggestions made in my previous post have helped resolve the issue. If the issue still persists, please do share more details about the issue. Thanks.


    Regards,
    Koteshwar Rao