looking for a 12v 5uA clock

Discussion in 'General Electronics Chat' started by whtupdo, Mar 31, 2008.

  1. whtupdo

    Thread Starter New Member

    Jan 16, 2008
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    0
    I'm looking for a 12v <5uA clock/oscilator. Does anyone ave any ideas?

    This oscilator is going to be used in an automotive application during sleep mode. The only voltage available during sleep mode is battery, 12v. I can't put a voltage regulator circuit in because it will draw more current. The max current I am allowed is 5uA.

    thanks for the help!
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    4000 series CMOS is about the only choice for 12 volt logic. You might try a phase shift oscillator made around a CD4011. Don't know if you can get to 5 uA, which sounds unrealistic. You didn't mention a frequency, so you'll need to figure the RC combination that will work. Don't expect really tight frequency stability.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    What kind of clock do you need?

    The CD4045 is a 21-stage counter that can use a 2.097152MHz crystal with support components to produce a pretty accurate 1Hz clock - quiescent current is 5uA @5v, 10uA@10v though. A high-efficiency buck-type regulator might get you close to your power budget, if you kept Vdd just below 5v.
    It just provides a clock, no register.
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    The 4060 will come close with the addition of a flip flop and an inexpensive watch crystal. I've never built this circuit, I picked it out of data book.

    [​IMG]
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    The 4060 looks like a better solution than the 4045. I took a look at ONSemi's datasheet for the MC14060, and it even has formulas for calculation of quiescent + dynamic current, which is very convenient. But it looks like in order to meet the 5uA budget @ 12v, the crystal will need to be around 7.3kHz or less. (Formula bottom of page 3 of the datasheet, It)

    Another obstacle is temperature. If you look at Idd(quiescent), it's small fractions of microamps @ 25°C. Those numbers go up quite a bit when you warm it up. There is also the frequency drift due to temp. You could minimize the drift with temp-compensated components in the tank circuit.
     
  6. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
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    nevermind.. i thought it was 500uA
     
  7. whtupdo

    Thread Starter New Member

    Jan 16, 2008
    8
    0
    Thanks for the quick replys. I'll take a look at the 4060, that looks like what I need.

    The clock does not have to be very acurate at all. It will be used to wake up a module at different intervals.
     
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