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C6745 Boot Issue

Patrick McNamara
Prodigy 220 points

My customer is having an issue with booting C6745 (TMS2C6745-BPTP3).   About 20% (120 of 700 in production run) of the devices fail to boot.  They measured 20 ohms to ground on VSS.  The working units measure 0.25 ohms.  If  they ground the pin then they work.  Is this ok/recommended to do this??

  • 0
    TI__Guru* 84110 points

    Patrick,

    I hope you are leaving out some very important information, such as exactly from where and to where 20 Ohms is being measured. Which pin do they ground to get it to work? The way your post is worded does not sound correct, so I think I need to understand a little more detail.

    Regards,
    RandyP

  • 0
    TI__Guru* 83745 points

    Hi Patrick

    As requested by Randy, request you to elaborate further.

    By ground did you mean OSCVSS or board VSS? 20 ohm seems high for a VSS connection, so it would be good to understand how it is being measured.Can you also share how the crystal is connected on their board and if the crystal meets the spec/requirements that are in the C6745 datasheet

    Regards

    Mukul

     

  • 0 in reply to Mukul Bhatnagar
    Prodigy 220 points

    To clarify....  The 22 Ohm resistance theyare seeing is between the OSCVss pin (144) and the Vss ground pad, it should be ~ 0 Ohms.  There appears to be a path through PLL0_VSSA to the external PLL ground.  If the external ground on PLL0_VSSA is removed, then the resistance is >20K Ohm from OSCVss to the Vss ground pad, and the resistance from OSCVss and PLL0_VSSA is 22 Ohms.  The crystal oscillator and PLL supplies are wired exactly as shown in the TI data sheet.  Thanks.

  • 0 in reply to Patrick McNamara
    TI__Guru* 83745 points

    This issue is being discussed offline via TI Sales Support channel (James Rose) and the customer.

    Regards

    Mukul