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AM1806: USB0_DP voltage at disconnecting USB cable

Expert 5545 points

Replies: 5

Views: 91

Part Number: AM1806

Hi Expert,

My customer found the around 2.7V voltage on USB0_DP pin at disconnecting USB cable.

Is it any problem? It seems to be leaked via USB ESD protection IC(TPD2E001DRLR).

Thanks

Muk

5 Replies

  • Hello Muk,

    There is a known leakage path from VBUS to the 3.3V supply rail.  Please refer to the AM1x schematic review checklist, specifically section 2.4.8.4.1 that discussed this and recommends isolating the input USB0_VBUS from the VBUS until the device is powered up using a discrete load switch.  Examples are shown in the document here:

    http://processors.wiki.ti.com/index.php/OMAP-L13x_/_C674x_/_AM1x_Schematic_Review_Checklist#USB_Board_Design_Guideline

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    Best regards,
    Jeff

  • In reply to Jeff Culverhouse:

    HI Jeff-san,

    If the USB connector is unplugged while power is being supplied to the AM1806 (USB PHY), the voltage of USB0_VBUS will be maintained at about 2.7V.
    It seems that it leaked from the USB ESD protection IC (TPD2E001DRLR), but is there any functional problem?

    Thanks

    Muk

  • In reply to Yusuke Mukuno:

    Hello Mukuno-san,

    We are not sure why the VBUS would drop to 2.7V when the cable is unplugged.  How are you controlling the VBUS voltage?  

    2.7V is within the VB_SESS_VLD so the OTG device will not initiate an SRP when plugging in, so not sure how the VBUS will go back to 5V?

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    Please click the Verify Answer button on this post if it answers your question.
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    Best regards,
    Jeff

  • In reply to Jeff Culverhouse:

    Hi Jeff-san,

    I sent e-mail about the customer schematics. please refer the schematics.

    Thanks

    Muk

  • In reply to Yusuke Mukuno:

    Hello Mukuno-san

    If this 2.7V comes from the ESD leakage, only way I can see this happens is the device is not disabling its DP or DM pullup when VBUS from us is off. If this is the case, then the device is not following the USB spec and we can’t guarantee anything with a non-compliant device.

     

    Electrically we may be ok with the PHY still powered on.  

     

    Is the TPS22913 on or off? If it is off, I wonder how it will handle with a 2.7V driving its input in its off state

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    Please click the Verify Answer button on this post if it answers your question.
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    Best regards,
    Jeff

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