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SN74AHCT16245: question on overshoot tolerance on I/O pins

Tom McTaggart
Intellectual 345 points
Part Number: SN74AHCT16245

We have signal integrity concerns with a particular circuit that uses this part. We may have both positive and negative going overshoot applied to its I/O pins when the part is in tri-state. From the data sheet, it appears that it may be able to clamp voltages on I/O pins to 0.5V of the rails, assuming the limiting current is not exceeded. Are we safe to use the part in this condition? Are there true diodes on the I/O pins, or some other structure....looking for engineering insight, not a guarantee, thanks!

  • 0
    TI__Guru* 96711 points
    Hi Tom,
    The internal parasitic clamp diodes to ground, found on the inputs and outputs of all CMOS logic, bleed off some of the overshoot current, but this parasitic clamp does not have the necessary frequency response to perform effective diode termination in high-speed applications. If you are seeing overshoot beyond the device's absolute maximum ratings (-0.5V to 7V) I would recommend an external high speed clamp diode to protect the device -- or series damping resistors at the signal source.