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Crystal Oscillator using SN74HC04 does not work !

Nguyen Thanh
Prodigy 10 points
Other Parts Discussed in Thread: SN74HC04, SN74HCU04

Hello Everybody,

I build this crystal oscillator  circuit like the diagram below. When I use IC HD74HC04 of Hitachi Semiconductor or 74HC04 of NXP semiconductor (formerly Philips semiconductor). It works well. But when I use SN74HC04 of Texas Instruments. It does not work ! Could anyone give me any suggestion ? Thanks.

  • 0
    TI__Guru**** 153186 points

    Moving to Logic for best support.

  • 0
    TI__Genius 14485 points

    Thanh,

    Good question. Please see the application note below. You will want to use a device that ends in "U04." Those devices are inverters with unbuffered outputs. Consider using the device SN74HCU04 in your application.

    http://www.ti.com/general/docs/lit/getliterature.tsp?literatureNumber=szza043&fileType=pdf

  • 0 in reply to James Lockridge19
    TI__Genius 14485 points

    Thanh,

    I also received the answer below as well. Apparently any inverter should work.

    "There are a couple of reason it may not work. The oscillation is based on holding the part in the threshold so if the threshold is slightly different the part will not oscillate.  This can even be true when another fab lot comes along.

    This is not usually real critical and most of the time parts can use the same RC. But if they are using a crystal The crystal capacitance is very critical. The crystal has a very tiny window of capacitive load where it will work. So a difference in Cin can make it not oscillate."

    In a lot of cases they will need to adjust their external c load. C1/C2 below."

     

  • 0
    Prodigy 20 points
    I would try a CD4069UBE or CD4049UBE - unbuffered. remeber not to leave inputs and outputs floating. I was under the impression that the 4049 does the `logic level conversion'. I usually just use the cd4069ube at a well regulated 5 volts. Try adding talantium (sp) capacitor on the supply rail for better filtering... 12 Mhz to me seems rather high - dunno how these would hold out. I usually try using Ceralock resonators. They have some great data sheets - ceralock that is...