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SN74LV1T34: Overshoot And Undershoot specification for 2.5V input

ASHISH BHANDARI
Prodigy 160 points
Part Number: SN74LV1T34

Hi,
I am using  SN74LV1T34 Logic level shifter for performing Up Translation from 2.5V to 3.3V.

1. An 2.5V signal from another device is fed to the input pin of SN74LV1T34. I want to know what is the Overshoot and undershoot limit for 2.5V signal at input pin(Pin no. 2).

2. Does 2.5V and 3.3V signal support 25MHz and 50MHz transfer ?

Thanks,

Ashish

  • 0
    TI__Mastermind 44470 points
    Hi Ashish,

    The overshoot limit is 5.5 V and the undershoot limit is determined by the VIH spec for 3.3 VCC in section 6.5 of the datasheet. Yes this device should handle that frequency no problem. Make sure to keep the load capacitance minimal as possible.
  • 0
    Prodigy 160 points

    Hi Dylan,

    Thanks for your response. But I need further insight on this.

    1. As per your  reply - "Overshoot limit is 5.5v" does it mean that a 2.5v signal can have a overshoot peak upto 5.5V?

    2. For undershoot - " undershoot limit is determined by the VIH spec for 3.3 VCC in section 6.5 of the datasheet". The section 6.5 in data sheet specify the High and Low level input voltage (VIH/VIL).How it is related to undershoot?

    Please refer the below image for reference.

    Sorry if my understand in wrong.

    Thanks in Advance,

    Ashish

  • 0 in reply to ASHISH BHANDARI
    TI__Mastermind 44470 points
    Ashish,

    Your image didn't link right, but I can break it down for you.

    1. For this I am referring to the input limitations to the device found in section 6.3 of the datasheet. The device input can handle voltages up to 5.5V so therefore it could handle an overshoot up to that voltage safely.

    2. The same applies for undershoot. If you have a 2.5 V high signal coming in and your supply is at 3.3V (since you are translating to that voltage) then you need to stay above the VIH spec (@ 3.3V VCC) of the device so the device reads the input as a high. Therefore, if your input signal has an undershoot it needs to stay above the VIH in order for the device to read it as a high still. If the undershoot goes below the VIH spec then the device could interpret the input as a low and switch low at the output.

    I don't expect the undershoot or overshoot to be that drastic, but in case it is, it will be up to you to control that to maintain the input signal within the correct input parameters of the device for it to work properly.
  • 0 in reply to Dylan Hubbard
    TI__Mastermind 44470 points
    Ashish,

    I saw your image on the other post and it helps me see what you are saying. Everything I said above is correct for when the signal is a logic high.

    From your image you are concerned with the undershoot for a logic low. For that, you want stay above -500 mV. For overshoot of logic low you want to stay under the VIL spec (@3.3 V).