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SN74ABT240A: Operating over recommended voltage

Brian Wang0928
Genius 14260 points
Part Number: SN74ABT240A
Other Parts Discussed in Thread: SN74HCS240, SN74AC240, , SN74AHCT240

One question for the voltage derating of the VCC bias power.

In application, the typical bias power is 5.25V connected to VCC pin that is generated from system aux power and Flyback. In application, the Over voltage protection is set to 5.9V and the trigger timing is about 1.5uS. 

Assume that the 5.9V transient voltage is happened at VCC pin and with 1.5uS then protected. Is VCC pin able to be derating with that?

one more, Is there any life decay when VCC bias power is operating over the recommend voltage of 5.5V? If so how is the decay diagram?

thanks !

regards

Brian

  • +1
    Guru 317770 points

    The absolute maximum rating is 7 V, so the device will not be damaged. Also see the footnote at the bottom of p. 2:

    Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated under “recommended operating conditions” is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.

  • +1
    TI__Mastermind 39425 points

    Hi Brian,

    Clemens' answer is correct.

    I would just like to add that TI does not guarantee functionality over "recommended op conditions". Anything that happens above that, TI does have have liability, it is "go above at your own risk" and even more so at abs max rating at 7V. 

    We do not have a decay diagram for these kinds of overvoltage. 

  • 0 in reply to Albert Xu1
    TI__Genius 14260 points

    Hi both, thanks.

    In real design, the over voltage protection on customer system is set at 5.9V by high side switch of TPS2662xx. it looks TI doesn't guarantee functionality with SN74ABT logic when VCC > 5.5V, correct?

    if so, what else similar logic device with high voltage you suggested? thanks. 

    Regards

    Brian

  • +1 in reply to Brian Wang0928
    Guru 317770 points

    SN74HCS240 or SN74AC240 work with up to 6 V, but they have different electrical characteristics.

  • 0 in reply to Clemens Ladisch
    TI__Genius 14260 points

    Thanks Clemens. 

    Is there p2p device with SN74ABT240A? And the Upper ESDs are not integrated at Input and Output rails for functional safety requirements as below.

    Regards

    Brian

  • 0 in reply to Brian Wang0928
    Guru 317770 points

    The SN74AHCT240 has overvoltage-tolerant and TTL-compatible inputs, but a lower drive strength.

    What are the actual requirements? Why was the SN74ABT240A chosen in the first place?

  • 0 in reply to Clemens Ladisch
    TI__Genius 14260 points

    The SN74AHCT240 also integrates the pull-up clamp diode at output side of device since functional safety concern. Pls find below diagram. Thus this device can not be used on products.

    Could you kindly support what suited one you can recommend? 

    Regards

    Brian

  • 0 in reply to Brian Wang0928
    TI__Mastermind 39425 points

    Hi Brian,

    If you cannot have an output clamp diode, unfortunately there aren't any good alternatives to the ABT device. 

  • 0 in reply to Albert Xu1
    TI__Genius 14260 points

    Hello Albert,

    Thanks. Customer is facing the challenge from Germany TUV on this matter. It looks that customer can only go with SN74ABT240A if there is no alternative one. 

    In the d/s, it says that the device could not be functional operation when VCC is fall in the range of the 5.5V to 7V, correct?

    Is there workaround way to convince TUV? thanks.  

    Regards

    Brian

  • 0 in reply to Brian Wang0928
    Guru 317770 points

    There is no specific technical reason for the 5.5 V limit; 5 V ± 10 % just are the traditional specified tolerances for TTL supplies. It is likely that voltages a little above 5.5 V will work. However, there is no guarantee whatsoever.

    If the device must work during transient overvoltages, then the only way to make the TÜV happy is to design the clamping to never exceed 5.5 V.

  • 0 in reply to Clemens Ladisch
    TI__Mastermind 39425 points

    Hi Brian,

    To go off Clemens' answer, the 5.5V max in the rec op conditions is for TI liability reasons. While the device may function above 5.5V, the customer will entire an area where they are out of warranty and liability will fall on incorrect usage of our device.