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SN74CB3T3253: The level of the output B terminal has 2.2V level, which is inconsistent with that of the input A（3.3V）

dang jinfa
Prodigy 120 points
Part Number: SN74CB3T3253

1、SCH

2、 S0=1，S1=0，1OE=0，2OE=0

3、The output level is related to the output pull-down resistance, and the test waveform is different for different pull-down resistance

  • 0
    TI__Genius 14350 points

    Hello dang,

    Please checkout this e2e post which explains more on this topic as I believe I answered a very similar question yesterday!

    Regards,

    Kameron

  • 0
    Prodigy 120 points

    Kameron~Thanks a lot 

    "So the reason why you are seeing this behavior is because the pull down resistor of 10K is sinking a large amount of (3.3V/10K= 330ua) current and affecting the Ron of this device"

    -----Can you explain in detail how the sinking current is affecting Ron?

    ------TI's  level shifting chip has a similar phenomenon?Whether there will be leakage current  if there is a pull-down resistor?

    ----  Is a p2p replacement for the SN74CB3T3253 device (FET only and no level shifting)?

     

  • 0 in reply to dang jinfa
    TI__Genius 14350 points

    Hello Dang,

    1. So section 5.4 off this appnote explains in greater detail how the Ron CB3T devices works.  A simple rule to remember for this device is "As the output current increases, Ron decreases.

    These graphs from the datasheet show what I mean in greater detail.

    2.All Ti analog multiplexers in the CB3T family will have the same phenomenon when there is a pulldown resistor( there will be "leakage" current) If you would like to know more about other TI translator devices I can forward this thread to another team.

    3.Yes SN74CB3T3253 is a normal FET without the level shifting. For example if your supply is 3.3V  when you pass a 3.3V signal in you should see approximately 3.3V on the output.

    Please let me know if anything is confusing and I am happy to help in any other way needed!

    Regards,

    Kameron