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SN74CBTD1G384/5 – About Tolerant I/O function

Guru 21040 points
Other Parts Discussed in Thread: SN74CBTD1G384, SN74CB3Q3305



Does SN74CBTD1G384/5 have “Tolerant I/O function”?

Our customer would like to input voltage to I/O pin at VCC=0V.

I suppose that it hasn't Tolerant I/O function.

Could you please give us your advice.




  • The I/Os will be High impedance when Vcc = 0V.

  • Hi


    Thank you for your reply.

    If input 5.0V to Input pin at VCC=0V , does SN74CBTD1G384/5 fail?

    My customer needs a function such as " 5-V Tolerant I/Os With Device Powered Up or Powered Down" of SN74CB3Q3305.

    But, I suppose that SN74CBTD1G384/5 hasn't this function.

    Therefore, I think that SN74CBTD1G284/5 fail.






  • The CBTD devices are 5V to 3.3V translators. The Vcc should be 5V so when Vcc is 5V they are 5V tolerant on the inputs and the output will be 3.3V. Sinc they are simple Nchannel FET's they willl be off when Vcc = 0V and there will be no leakage so even though they do not have Ioff spec their I/O's willl be high impedance when Vcc is 0V.This means they can have 5V on the I/Os when Vcc is 5V or when Vcc is 0V. One thing to remember about CBTD is that they can not run at very high frequency.

    CB3Q has the Ioff feature so it can also is 5V tolerant with Vcc powered up or powered down but its Vcc can go lower than CBTD.

    If you want to translate from 5V to 3.3V then you should consider using a CB3T device like SN74CB3T3306. They can operate at higher frequencies than CBTD.


  • Hi


    Thank you for the information.

    I understood that SN74CBTD1G284/5 can input 5.0V to I/Os when VCC is 0V.

    Thank you very much.