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TM4C129CNCPDT USB maximum ratings

Luiz Mellucci
Prodigy 210 points
Other Parts Discussed in Thread: TM4C129CNCPDT

Hello,

We are using the USB of TM4C129CNCPDT microcontroller in full speed mode. At end of packet (EOP) signalization we have voltage spikes at data lines over common I/O  limit (300mV).

Despite it, this interface is made to interface directly USB devices and maybe it can withstand harder limits than common I/O limit.

Does microcontroller USB data lines have differentiated limits than common I/O? If yes, where can I find it?

Thanks,

  • 0
    Genius 4680 points

    At end of packet (EOP) signalization we have voltage spikes at data lines over common I/O  limit (300mV).



    At EOP (SE0, single-ended zero) and inter-packet period after EOP, single-ended spec of the bus is applied to the D+/D- lines. No "common I/O limit" is specified in this period. Also, differential common mode range (Vcm) of full-/low-spped bus is 2.5V max by the USB2.0 spec.

    Tsuneo

  • 0 in reply to Tsuneo Chinzei
    Prodigy 210 points

    We are not talking about the same thing. I'll try to be clearer.

    Regarding microcontroller TM4C129CNCPDT, which is the maximum ratings (negative and positive) for transients at USB data pins?

    We are observing spikes of -660mV x 15ns spike. Datasheet says that maximum rating for I/O pins are -300mV, but there is not a specific value for USB data lines or for transients.

  • 0 in reply to Luiz Mellucci
    TI__Guru**** 244400 points
    Hello Luiz,

    The USB IO's are same as other GPIO's. So any electrical value specified for GPIO would be applicable to USB IO's as well.

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Prodigy 210 points

    Hello Amit,

    Thanks for your reply.

    I understand that the -300mV maximum rating is a secure level for DC or long transients. But is it the same limit for nanosecond transients (figure below)? Energy in this case is very small with smaller damage potencial.

    Luiz

  • 0 in reply to Luiz Mellucci
    TI__Guru**** 244400 points
    Hello Luiz,

    I believe looking at the scope snapshot of the transient, the ESD must be working on this transient to safeguard the TM4C device.

    Regards
    Amit