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SN74AHC00 / Delay time from VCC powered up to valid output

S.Satoshi
Guru 21675 points

Hi All,

Our customer need to know the delay time from VCC powered up to valid output. Should we assume that it almost the same with tPLH or tPHL though there is no POR circuit in the logic devices like this?

Best Regards,

Sonoki / Japan Disty

  • 0
    TI__Mastermind 46480 points

    We do not normally measure this. The part will actuall begins to function before the part reachas a valid Vcc so I am not sure how you would measure this. Most power supply rise times are very slow in the Us range but the Vcc can also be controlled by a switch pr sometheing where the power up ramp is very fast so it is hard to say where you how you would measure this delay time.  I think that if you allow a TPD from the time the power reaches a valid state you would be safe.

  • 0 in reply to Chris Cockrill
    Guru 21675 points

    Hi Chris-san,

    Thank you for your quick response. I understand what you commented and also expected such comments. I understand that the propagation delay from part reaches a valid VCC to output must be present in logic devices, but it may become pronounced depend on the rise time of VCC.

     

    Best Regards,

    Sonoki

     

  • 0 in reply to S.Satoshi
    TI__Mastermind 46480 points

    Hi Sonoki-san

     I am not sure if rise time effects it or not. I dont have nay data to prove it one way or the other.

    At some point the part will begin to function, usually before it reache the specd min Vcc. This is usually about 1.5V.

    Then the output will follow the Vcc. I suspect it is about a tpd between the two.

    I don really know tha answer to this? 

    The voltage level  where th part begins to work will be similar to a threshold and can vary from normal process variations.