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TMS320F28377S: Input of undershoot exceeding the lower limit of the absolute maximum rated "Input Voltage"

Sh.Sasaki
Guru 13625 points
Part Number: TMS320F28377S

Hi all,

My customers recognize that input of undershoot exceeding the lower limit (-0.3 V) of the absolute maximum rated "Input Voltage" listed in the datasheet is out of warranty.

So please teach me about the followings.

I think the clamp diode exists at the IO port.

I want to know the reference value that can be input on the assumption that this is not conducted.

In the customer's system, there is a possibility that a voltage of -0.475 V is input to the device for 1.32 nsec.

Best regards,

Sasaki

  • 0
    TI__Guru 60865 points
    Hi S.Sasaki,

    -0.3V is the level where essentially no current will ever be conducted.

    After -0.3V, the question is "how much current?". This mostly depends on the series R on the pin.

    e.g. If we assume a perfect diode switch which conducts nothing until 0.3V and then infinite current >0.3V, if the pin had 50-ohm series termination and the voltage is -0.475, then the max clamping current is (-0.3 - -0.475)/50 = 3.5mA. The max clamping current specification is 20mA (total for the device) so this would probably be OK as long as it only occurred on one pin.

    The above is worst-case. Realistically the diode threshold will not be quite that low (even at worst case voltage, temperature, and process) and it won't conduct infinite current right at the threshold voltage.
  • 0 in reply to Devin Cottier
    Guru 13625 points
    Hi Devin-san,

    Thank you for your support!
    I got it!

    Best regards,
    Sasaki