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SN74LV125A datasheet VS. SN74AHC125 Datasheet

R11
Expert 1485 points
Other Parts Discussed in Thread: SN74LV125A, SN74AHC125

I saw the following parameter in the SN74LV125A datasheet which was not in the SN74AHC125 datasheet.  Is the SN74AHC125 capable of the same thing or is only  the SN74LV125A capable of having a voltage present on the output when the device is unpowered?

Voltage range applied to any output in the high-impedance or power-off state, Vo (see Note 1).......   -.05V to 7V 

Also, are there recommended packages (in terms of availability) for the SN74LV125A and 125AT?

  • 0
    TI__Mastermind 45250 points

    Rustin,

    The outputs of these two devices are different as you have noticed.

    The main difference is that the SN74LV125A does not have a protection diode to the Vcc rail. This is indicated in the spec in that the maximum voltage is rated at the max supply voltage and not beyond Vcc. There is no Vcc + 0.5V as shown in the SN74AHC125 data sheet. This (+ 0.5V) indicates that a diode is present to the Vcc rail in the AHC125 part.

    This lack of a protection diode is also confirmed in that the output clamp current is only mentioned for the Vo < 0V in the LV125A. In the AHC125 it is shown +/-  20 mA.

    Because there is no protection diode to Vcc in the LV125A part, it can have a voltage on the outputs when the part is not powered without an issue. It just cannot exceed the maximum voltage listed.

    If the AHC125 part was used in this manner, it would conduct the output voltage to the Vcc (un-powered) rail through the protection diode.

    I cannot really speak to the availability issue. It would be better to contact your TI sales rep or your distributor. They would be better prepared to answer this type question.

    Please let me know if you have any additional questions.

    Richard Elmquist