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SN74ACT245: Does VCC+0.5V of the maximum input voltage range vary with VCC?

rengui sun
Intellectual 680 points
Part Number: SN74ACT245
Other Parts Discussed in Thread: SN74LVC245A

The input voltage range in the maximum parameter in the datasheet is -0.5V~VCC+0.5.

When the power supply voltage of the SN74ACT245 is 0V, the input voltage is 4V, which will damage the chip？If so, what are the consequences of damage? Does the whole chip fail or is the input pin open?

In the system, the SN74ACT245 uses 3.3V power supply. When the 3.3V power supply is not started when the system is powered on, the input voltage of the SN74ACT245 is already 4V. Duration is about 100ms. No problems are found in the current use.

  • 0
    TI__Mastermind 44570 points
    Hi Rengui,

    The notes below the abs max table provide some helpful information on this. These are stress ratings so yes there is a good chance of damage violating these specs. It'll most likely damage the input ESD structure of the device as current will flow through diode. The notes also state that the input voltage range can be exceeded if the current is monitored and maintained below the Iik spec. This is most likely the reason you haven't seen any problems. However, I don't recommend this device here since you are still violating the spec when it's powered to 3.3 V and the input is at 4 V. Id use the SN74LVC245A here instead. It can operate at 3.3 V and its inputs are 5.5 V tolerant.
  • 0 in reply to Dylan Hubbard
    Intellectual 680 points

    Hi Dylan,

    Because the Spring Festival holiday, the reply is late, I'm sorry.

    Does the input of SN74LVC245A have a positive clamp diode? The  abs max table only provide  the  input clampe current of negative diode.

  • 0 in reply to rengui sun
    TI__Mastermind 44570 points
    Hi Rengui,

    No worries, I hope you had a great holiday! The SN74LVC245A does not have positive clamp diodes. This is one of the factors that enables this device to have 5.5 V tolerant inputs.