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LSF0108: LSF-EVM

Jacek Kupinski
Intellectual 360 points
Part Number: LSF0108
Other Parts Discussed in Thread: LSF-EVM, , SN74LVC1T45

Hi I am looking for a basic level translator function from 3.3V to 5.0V standard.

I selected the evaluation board LSF-EVM hoping for a easy solution yet got a problem. It needs to drive  50Ohm impedance too.

this part when connected to the scope with 50ohm input Voh drops to ~ 1.2V 

would you recommend different part that would meet those requirement ideally with the eval board and eval board with sma connectors on it?

Thanks,

Jacek Kupinski

  • 0
    TI__Guru* 97016 points

    Hi Jacek,

    Logic devices won't be driving a 50 ohm load -- they are designed to drive a capacitive (high-impedance) load. What exactly are you trying to do?

  • 0 in reply to Emrys Maier
    Intellectual 360 points

    I have a 3.3V level trigger source but want to drive a 5V level base laser that has a low impedance 50Ohms input [trigger frequency of few MHz] so need lavel translator + device that is capable of driving 50Ohm so that's why I selected LSF0108. Is there anything else you would recommend?

    Thanks,

    Jacek   

  • 0 in reply to Jacek Kupinski
    Guru 300430 points

    The LSF is a passive switch; its high-level voltage is determined only by the pull-up resistor.

    What voltage do you need at the laser? (5 V would require an infinitely high drive strength.)

    A buffered level shifter like the SN74LVC1T45 has an output impedance of about 12 Ω; you can add a series resistor to increase it to 50 Ω, if that is what you want.

  • +1 in reply to Clemens Ladisch
    Intellectual 360 points

    Thanks, I'll try your suggestion

    Jacek