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SN74HC245PWRG4 input voltage protection

Rex Walters
Prodigy 40 points

A previously designed instrument has a SN74HC245PWRG4 part  with a 3.3V VCC designed in.

The B side pins are used as inputs have a series 1K resistor which are connected to a connector for an external interface.

The data sheet mentions something about an input clamp.

Can a 5V signal be applied to the series 1K resistor and not cause damage to the SN74HC245PWRG4 with VCC at 3.3V?

  • 0
    TI__Guru 57390 points
    Hi Rex ,

    I would not suggest this , although , probably it wont be damaging the device since you have a 1K series current clamp resistor .
    The reason being that the inputs and outputs on this device has ESD diodes to Vcc ,which means that any voltage above Vcc+0.5V would turn on the diodes . Unless the clamp current is well below the input/output clamp current as per the abs max table, it might cause permanent damage to the device . It would also accidently power up the device with input /output signal present on the lines when Vcc is 0V too .