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SN74LV1T126: Output Impedance when no VCC is applied

Part Number: SN74LV1T126
Other Parts Discussed in Thread: SN74LV1T34, SN74LVC1T45, SN74AXC1T45

I have the requirements of maintaining output Hi-Z when levelshifter is not in use. And in this case, VCC will be switch OFF.

I have tried non-tri-state version, SN74LV1T34.. It dose not work. That's why I want to use SN74LV1T126.  Can I tied resistor fromm VCC to OE to control the Hi-Z when VCC is gpne??

However,  it seems that specifications not actually mentioned anything about the case when VCC is gone... 

Can you please clarify??

  • Hi Edmund,

    May I know the voltage levels required for translation? Would you consider using the dual supply translators like the SN74AXC1T45 or the SN74LVC1T45 which have Ioff protection and Vcc isolation circuitry built-in?
    For the input / output ports to ensure Hi-Z when Vcc is at 0V, the device must have Ioff partial power down mode feature. The SN74LV1T34 / SN74LV1T126 doesn't have this feature.
  • Also, Vcc left floating is different from Vcc held at 0V. The Vcc must be held at or close to 0V to ensure Ioff protection( hi-Z on IO ports).
  • Hi Shreya,

    I translate 5V to 3,3V. However, when power is OFF (not 0V, but I am not sure if there any discharge path when power is OFF), I need to connect the translator output to other devices.

    I don't need Bi-directional or directional control. 

    Do you think SN74AXC1T45 will be OK with my application? 

    BR,Edmund

  • If 0V is a must, would that be helpful to add some kind of breeding resistor on power rail? If so, do I need to add both at 5V and 3.3V??
  • Hi Edmund,

    The SN74LVC1T45 device which supports Ioff should work for you. The SN74AXC1T45 doesn't accept voltages beyond 3.6V.
    Again, Ioff cannot be guaranteed when the Vcc pin is left floating and not held at gnd.