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USB ESD Protection for TM4C part

JR Simma
Intellectual 660 points

Other Parts Discussed in Thread: TM4C123GE6PM

I'm having trouble finding 100% fool proof USB device ESD protection for TM4C parts.  Per the datasheet, the USB D+ and D- lines are limited to 3.6V, but it seems like most TI solutions will limit voltage to 3.7V, which of course doesn't meet TI's requirements.

The device we are dealing with is a TM4C123xxx.  The situation we are concerned with is as the USB connector is connected, all 4 pins won't connect at the same time.  So assume, for this problem, that D+ and GND are the first two connected.  From the looks of most TI's ESD protection IC's, the D+ line could exceed 3.6V.  However, maybe I've missed some ICs or other parts.  Does TI offer some parts to limit D+ and D- to 3.6V under a ESD surge?  

  • 0
    TI__Guru**** 244440 points
    Hello JR,

    The USB DP and DM IO's have ESD protection on them as given in the Fail Safe Electrical section of the Data sheet.

    Regards
    Amit
  • 0 in reply to Amit Ashara
    Intellectual 660 points

    Amit:

    Thank you for your response.  On a side note, I'm not sure if PD4 and PD5 (USB pins) are fail-safe or non-fail-safe.  Below is a short copy from TM4C123GE6PM.  Also, Table 24-1 lists max voltage for pd4/pd5 as Vdd+0.3 (which I believe lines up with non-fail-safe).  However, app note spma053 lists USB pins as fail-safe.  Although I'm confused on fail-safe vs non-fail-safe, I only need confirmation that the ESD protection on PD4 and PD5 (USB pins) are protected when the device is unpowered.  When I say "unpowered", I mean VCC is floating, but ground is connected and there is a ESD spike on either PD4, PD5 (USB), GND.  Or if VCC is connected, but ground is floating, and there is an ESD spike on PD4, PD5 (USB).

    24.13.2

    With respect to ESD and leakage current, three types of I/O pins exist on the device: Power I/O
    pins, I/O pins with fail-safe ESD protection (GPIOs other than PD4 and PD5 , and XOSCn pins)

  • 0 in reply to JR Simma
    TI__Guru**** 244440 points
    Hello JR,

    The USB pins are fail safe.

    Regards
    Amit