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3.3 to 5 volt interface

Discussion in 'Electronic Design' started by newinwa, Aug 16, 2006.

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  1. newinwa

    newinwa Guest

    Anyone know of a really simple way to drive a 3.3 volt output into a 5 Volt
    device?

    I need to be able to a 50Mhz clock into a 5 volt device and it's surprising
    difficult to do this...

    thanks...
     
  2. Fred Bloggs

    Fred Bloggs Guest

    NO IT IS NOT! Even a CMOS 5V input requires no more than 5
    x(0.7-0.3)=2Vpp for guaranteed operation, and you have probably 3Vpp.
    Bias the 5V input at 5V/2 DC, with a resistor divider, and ac-couple the
    clock into it, with a capacitor.
     
  3. DJ Delorie

    DJ Delorie Guest

    Transistor? If you don't mind inverting the clock. Else, two
    transistors. Total cost, about $0.30.

    How about a SN74LVC1G06 ? It's a single open drain buffer in sot-23 or
    sot-323 packaging, runs on 3.3v or 5v Vcc, and accepts either 3.3v or
    5v logic input. Use a pullup to whatever Voh you need. About $0.44.
     
  4. 74LVC4245
     
  5. almo

    almo Guest

    DC--DC step-up converter, maybe? (Not sure if I read the whole
    question.)
     
  6. Howard

    Howard Guest

    Use a pull-up resistor at the input and a diode between the two devices
    (anode to input of driven device and cathode to output of driving
    device).

    HS
     
  7. Tam/WB2TT

    Tam/WB2TT Guest

    If the 5V device has TTL input thresholds, you don't have to do anything.
    For instance, a 3.3V device can drive a 74ACTxxx directly. If you can't pick
    the 5 V device, use a 74ACT32 as a buffer.

    Tam
     
  8. newinwa

    newinwa Guest

    Thanks for the diode idea ..I was thinking about that one today.
    Have to be a pretty fast diode tho...

    I have ZLL400 that might do...I'll try that

    The thresholds are Vih=3.5V Vil=1. The 3.3 oscillator works but is out of
    spec...and not available in 5 volt (its spread spectrum)

    thanks again for your thoughts
     
  9. Fred Bloggs

    Fred Bloggs Guest

    Typical- the nitwit zeroes in on the most wholly out-of-spec and
    worthless "solution."
     
  10. Typical - the twit dishes out sarcastic criticism without any hint of
    help.

    I have learned that people do best what they feel they are most capable
    of.
     
  11. Fred Bloggs

    Fred Bloggs Guest

    Yeah- and in your case that is absolutely NOTHING! You're a goddammed
    loudmouth heckling from the bleachers as usual. *I* already told him to
    use ac-coupling. Where is your post, you fat-faced lethargic pos?
     
  12. Q.E.D.
     
  13. Fred Bloggs

    Fred Bloggs Guest

    Is that the best you can do? Think so. You avoided answering where your
    post is because there was none. You're a typical spectator leach. Maybe
    you're that same passive-aggressive flake "Bob Monsen"- whatever, take a
    hike.
     
  14. You can be assured that my ability in your chosen field will always
    pale beside yours. Since my advice or examples will always be useless
    to you or to anyone who feels that your inputs are of value, then you
    should ignore me forever. Plonk me now!

    Is that passive-aggressive enough for you?

    Were you able to read between the lines?
     
  15. Fred Bloggs

    Fred Bloggs Guest

    You really have a certain gelatinous and spineless way of communicating,
    very much in keeping with your character , or lack thereof. You refuse
    to answer any questions put to you, because you are a sham of a man, and
    you refuse to acknowledge that your initial criticism of my
    participation in the thread was dead wrong, and actually more applicable
    to the likes of you. Somewhere along the way someone mislead you into
    believing your ideas, opinions, and say in matters was important.
    Whoever did that was either deceiving you or starved for babble. Why
    don't you go loiter down by the fountain at the mall like a good little
    retiree.
     
  16. Sorry, not retired yet.

    The reason I didn't reply with advice was that the method I would have
    suggested had already been presented. There were several excellent
    suggestion, most of them better than yours.
     
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