Selecting right digital buffer - 20us switching

Discussion in 'General Electronics Chat' started by Vindhyachal Takniki, Jan 1, 2015.

  1. Vindhyachal Takniki

    Thread Starter Member

    Nov 3, 2014
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    1. I have a microcontroller programmed to switch 16 I/O pins at 20us interval to drive certain load at each pin. I have to operate at 3.3V.

    2. Now I want to buffer the MCu pin from load with a buffer.'

    3. I have been reading about TI's SN74ALVC16244A. It is 16 bit buffer, with 3ns Tpd.

    4. What will be each pin max drive current when all pins are turning on at same time. Datsheet says +-24mA drive, is it for all pin together or individual?

    5. Any other better buffer?
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Per Pin. It may not be rated for paralleling all the pins because you might exceed the max current rating on the Vdd or Vss pin.
     
  3. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    The absolute max current for Vdd and Vss is 100mA. So, the total current of all the pins + the quiescent current should not go close to that, at least for long periods of time.

    There are also power dissipation issues. DIPs/SOPs don't dissipate power well. At 24mA, a pin drops 1v, giving 24mW power dissipation for just 1 pin.

    Depending on the app, you may be better off using individual FETs for each pin.
     
    absf likes this.
  4. Vindhyachal Takniki

    Thread Starter Member

    Nov 3, 2014
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    6
    I have to drive a npn transistor which is used as switch
     
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    So the 24mA per pin on the SN74ALVC16244A is not enough?

    What is enough?
    How much current do you need to switch?
    What is the open-circuit voltage that the switch has to handle?
     
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