Looking for part: Single 12v Schmitt Trigger

Discussion in 'Digital Circuit Design' started by Dr.Wizard, Sep 17, 2016.

  1. Dr.Wizard

    Thread Starter New Member

    Sep 17, 2016
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    0
    Hello All,
    I am looking for a particular part for a project, but can't seem to find quite what I'm looking for. I was hoping someone might know of a suitable part.

    I am looking for a single, non-inverting Schmitt trigger chip, similar to the 74LVC1G17 which will work on 12 volts. Several mfr's make versions of it for 5 volts. (Link is to the datasheet of the NXP version.) I have found several hex (6-per-chip) versions such as the CD40106BC which work with 12 volts, just can't find a single version. I am looking for a single 12v version a) because I only need one per location, and more importantly b) need the smallest possible part.

    FYI: This is to clean up and buffer the signal going to 12volt WS2811 pixels where the pixels are a long distance from the controller. They are finicky about the data signal and it is prone to noise on long runs. The typical solution is to install "ghost" pixels along the way, but I was looking to put a tiny chip on a 1/4" by 1/2" board which could be installed inline and covered with shrinkable tubing. Pixels are too big because the wire needs to get pulled thru conduit.

    Current plan is to just use SOP ws2811 chips with no LEDs, but Schmitt triggers would be even better if I can find them. The Schmitt will do a better job at cleaning up the signal. Unfortunately, the WS2811's do not include a Schmitt on the input. If they did, they wouldn't be so cantankerous about the signal.

    Can anyone suggest a part number?
     
  2. ian field

    Distinguished Member

    Oct 27, 2012
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    A single buffer gate with a bit of feedback might get you out of trouble.

    You'll probably need a resistor in series with the input, and selecting the right feedback resistor could be hard work.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,555
    2,375
    What about a simple comparator?
    Max.
     
  4. Papabravo

    Expert

    Feb 24, 2006
    10,152
    1,793
    I think you are SOL. I'm pretty sure the trend in single gate logic is to lower voltages. A multiple transistor array in a SOT-23 package could be an option. That way you could take a stab at a push pull output booster.

    Something like this:

    http://www.vishay.com/docs/71963/71963.pdf
     
  5. Papabravo

    Expert

    Feb 24, 2006
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    The open collector output might have too slow a rise time.
     
  6. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    Something like this (with different resistor values I should think):
    [​IMG]
    or an op-amp with positive feedback.
    Either of these with SMD would easily fit.
     
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,544
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    What is the frequency or minimum pulse width of the signal you want to regenerate?

    ak
     
    Last edited: Sep 18, 2016
  8. be80be

    Senior Member

    Jul 5, 2008
    431
    57
  9. Papabravo

    Expert

    Feb 24, 2006
    10,152
    1,793
    Not sure if the output is open collector(drain) or push pull, but the pullup resistor in the example test circuit suggests open collector and that might slow down the low to high transition. Check the propagation delay time as well.
     
  10. AlbertHall

    Well-Known Member

    Jun 4, 2014
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    It does say:
    "The detector circuit is optimized for
    simplicity of operation and utilizes an open collector
    output for maximum application flexibility "
    but also that it is designed for high speed up to 1MHz.
     
  11. Papabravo

    Expert

    Feb 24, 2006
    10,152
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    Speed is NOT the same thing as propagation delay and the distortion associated with the pullup resistor charging a capacitive load. The TS is the only one who can tell us if this will work or not and so far he remains silent.
     
  12. ian field

    Distinguished Member

    Oct 27, 2012
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    Sounds like the TS is thinking more along the lines of a single gate package - for an inverter/buffer; that can be a 4 pin SMD package not unlike the DG MOSFETs in a TV tuner.

    The TL431 is a comparator, but you are stuck with the internal 2.5V Vref. And its inverting - so feedback has linearising effect rather than making it snap-action. On the plus side; its available in SMD packages, and I believe there's a version with 1.25V Vref.
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I was thinking in terms of a variable Vref type.
    Max.
     
  14. ian field

    Distinguished Member

    Oct 27, 2012
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    Those have more pins.................
     
  15. Dr.Wizard

    Thread Starter New Member

    Sep 17, 2016
    3
    0
    Hello All,
    Thanks for all the suggestions! I got some good ones from another forum as well, although none of them is quite what I'm looking for. Size is an issue here since it needs to get pulled thru conduit. My hope was for a small SOP package that I could put on a narrow little circuit board and wrap with heat shrink.
    Best suggestions so far have been the opto-Schmitt which is a little larger than I had hoped for, but still within allowable range, and this part: http://rohmfs.rohm.com/en/products/databook/datasheet/ic/logic_switch/standard_logic/bu4s584g2-e.pdf which is an inverter, but I figure I can use them in pairs. One about 1/3 way down the cable, and another 2/3 the way down.
    I appreciate everyones ideas!
     
  16. Dr.Wizard

    Thread Starter New Member

    Sep 17, 2016
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    Speed by the way, is 400KHz. I'm also thinking of experimenting with cat5e cable and RG-6 coax. But I don't have an oscilloscope to check my results at the other end. A friend of mine just bought one of those cheap DS-203 pocket scopes. Not great, but good enough for this situation. I'm also wondering if I can convert it to a differential signalling system like RS-485 and then back again.
     
  17. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
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    That frequency could be pushing your luck with an optocoupler - you might just about get away with it if you can find a PD output type. Transistor output optos might be too slow, a darlington output will stop it dead in its tracks.
     
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