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SN74AVC4T774: About behavior when VCCB=0V

Guru 21045 points
Part Number: SN74AVC4T774

Hi Team,

 

We are evaluating SN74AVC4T774RSVR at the following conditions.

Case1: VCCB pin is 0V but if we input the 25MHz signal to B1 pin, VCCB becomes 2.5V.

Case2: VCCB pin is 0V if we input the low signal to B1 pin.

 

So, we guess that the voltage of B1 pin appears to VCCB pin.

Is this behavior right?


 

 

Regards,

Kanemaru

  • Kanemaru san,

    I believe this kind of behavior is unexpected with the SN74AVC4T774.
    The device has Ioff partial power down feature which will enable the I/Os to stay active while either of the Vcc is held at gnd. It prevents leakage from I/O ports to accidentally turn on the device through the clamp diodes.
    can you try to disable the OE pin and try to see if the issue persists ? can you try other devices , preferably from another lot in case you have the access?
  • When you mention that the Vcca / Vccb is at 0V , is the supply turned off(floating) or is it forced to 0V ?
  • Hi Shreyas-san,

     

    Thank you for your prompt reply.

    We will confirm the things below(your questions).

    -can you try to disable the OE pin and try to see if the issue persists ?

    -can you try other devices , preferably from another lot in case you have the access?

     

    When you mention that the Vcca / Vccb is at 0V , is the supply turned off(floating) or is it forced to 0V ?

    -> (My answer) the supply is turned off(floating). If it is floating, may a phenomenon of “case1” occur?

     

    Regards,

    Kanemaru

  • Kanemaru ,

    The Ioff feature requires the supplies to be held at or near 0V. floating node doesn't guarantee 0V. Case 1 is definitely a possibility.
  • Hi Shreyas-san,

     

    Thank you for the information.

     

    Regards,

    Kanemaru