[time-nuts] 32.768Khz Crystal/Resonator suggestions.

[Didier Juges]

It all depends on how accurate the frequency has to be. If you only need
2%, I would use a C8051F300 microcontroller's built-in oscillator (24.5MHz
+/-2%) and divide it down using the processor itself.
The chip comes in a 11 pin QFN that is 3x3 mm, a little bigger than you
need, but it does not require any external component.
The frequency can be trimmed to better than 2% on many Silabs chips but I
am not 100% sure that is the case on this one.



On Fri, Nov 1, 2013 at 11:30 AM, Dan Kemppainen <dan at irtelemetrics.com>wrote:

> Hi all,
>
> I've got a project upcoming that will require a frequency of 32.768 Khz
> in a harsh environment (Imagine a thousand G's at 100Hz with 150 Deg C
> temperatures). Also, this thing needs to be small, 2mmx1.5x1.5mm or so.
> It also has to be low power. Frequency stability is probably less of a
> concern than just surviving (some frequency error vs. temp can be
> trimmed out with other smarts in the design.
>
>
> In the past, crystals just haven't liked surviving due to the
> construction. Have had good luck with ceramic resonators at higher
> frequencies (50Mhz and up). I've also looked at silicon oscillators,
> which will work in the application, however with the chip and associated
> resistors/caps they get a little bigger that what I was hoping for.
>
> Is anyone aware of a frequency source (crystal/resonator or other) in a
> small package that is robustly mounted?
>
> Or are there any ceramic resonators available that are in small packages
> in those low frequencies? I checked the big distributors, and did not
> have any luck.
>
>
> Dan
>
>
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