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SN74LVC8T245 Input Tolerance

Tuan To
Prodigy 210 points
Other Parts Discussed in Thread: SN74LVC8T245

If VCCB of SN74LVC8T245 is connected to 3.3V power supply, can its I/O ports on B port (B side) be connected to TTL (5V) signals? Will the I/O ports be damaged?

  • 0
    TI__Intellectual 2060 points

    I would not recommend this without a current limiting resistor on the input.  The reason is that the input pins have diodes to VDD and VSS.  If the voltage input is outside of the VSS to VDD range then the diodes pull the voltage to the appropriate supply rail.  Having a large voltage difference at the pin can end up damaging these diodes because they are not meant to dissipate much power.  If the diode to VDD is damaged it will likely act as a short and the gate will be permanently positively biased.

    Regards,

    Mike