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CD4050B: 15 V to 3.3 V Translation with CD4050B

Varunesh Kumar
Intellectual 940 points
Part Number: CD4050B
Other Parts Discussed in Thread: CSD17571Q2

Tool/software:

Hello

I wish to translate +15 V signals to 3.3V to my DSP.

Can I use CD4050B for this purpose, where the Vdd is 3.3V 

( A similar IC from Onsemi MC14050 specifies a Vdd of 3 to 18 V )

If yes, how will the propagation delay be impacted?

What other choices do I have from TI's stable?

Thanks in advance 

  • 0
    Guru 316940 points

    CD4000 level shifters will work for this. But with 3.3 V at the output side, they will be very slow.

    Alternatively, you could built a discrete MOSFET level shifter. Use any 15 V MOSFET with a gate-to-source threshold voltage that is low enough even when the source is pulled low through the body diode, e.g., CSD17571Q2. The speed of rising edges depends on the pull-up resistor.

  • +1 in reply to Clemens Ladisch
    Intellectual 940 points

    Thank you Clemnens for your prompt replies, as always.

    I had a few signals requiring to be fed to the 3.3 V DSP

    and hence am inclined to use the new device TXH0137D-Q1.

    I have a question regarding that.

    I have a +15V supply which I can feed to its Vcc terminal.

    O/P side Pull up to 3.3V, how do I size the O/P Resistor 

    to keep the Prop Delay at around 250 nS, or is the Prop 

    delay only dependent on the Vcc ?

    Thanks in advance

    Varun

  • 0 in reply to Varunesh Kumar
    Guru 316940 points

    The TXH has open-drain outputs that use exactly the same MOSFET as in the discrete implementation.

    The speed of rising edges is limited by the low-pass-filter formed by the pull-up resistor and the trace/device capacitances. These capacitances are hard to estimate; it might be easier to check the waveform with an oscilloscope and to adjust the resistor.

  • +1 in reply to Clemens Ladisch
    Intellectual 940 points

    Thanks, Clemens for your prompt replies as ever.

    Yes, I shall do that with a Scope.

    BTW, this must be a rather common problem, with most DSP users

    to translate Signals to 3.3 V 

    Thanks again for your support.

    Varun

    ,