looking for a 12v 5uA clock

Thread Starter

whtupdo

Joined Jan 16, 2008
8
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!
 

beenthere

Joined Apr 20, 2004
15,819
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.
 

SgtWookie

Joined Jul 17, 2007
22,230
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.
 

Wendy

Joined Mar 24, 2008
23,415
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.

 

SgtWookie

Joined Jul 17, 2007
22,230
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.
 

Thread Starter

whtupdo

Joined Jan 16, 2008
8
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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