Hi,

I am using the CY7C68013A chip on our PCB, and was looking for an appropriate crystal to meet the required specifications as described in you application notes (point 4 on AN15456).

I am unable to find either crystal recommended in your app note or other crystals that meet the required specs of:

■ Parallel resonant
■ Fundamental mode
■ Frequency Stability: ±100 ppm
■ 500-uW drive level
■ 12pF (5% tolerance) load capacitors

Furthermore, the crystals used on the devboard CY3684 dev kit and the UPEK FISK USB reference design that incorporates the NX2LP chip (CY7C68033-56LFXC) do not meet the above specifications.

Could you please inform me whether it is necessary to use at least 500-uW drive level crystal, and whether I can use crystals with other load capacitances in my design.

Many Thanks,

Sach 

Yes. It is recommended to use a crystal with that specifications.

The part that is there on the FX2LP DVK is: ECS-240-20-4. I think this part is available. Please check.

Regards,

sai krishna.

 Can you please recommend a smaller package crystal that still meets the specs - the crystal you have sent me is very large!

Thanks

 Hi,

Another thing : the part you have recommended (as used on the dev board) has a 20pF load capacitance (where 12pF is recommended in the applciation note) - so am I right in thinking it doesn't matter what load capacitance crystal we use with the chip?

Thanks 

It has to do with the crystal startup. FX2LP has been extensively tested with 12pF load. So please use a 12 pF load.

Regards,

Anand

Hi Anand,

 I really don't get it though, why have you used a 20pF crystal on the dev board for FX2LP?    I would really appreciate it if you could even give me an example of a (small) part that has a load capacitance of 12pF and drive level of 500uW as none of our suppliers (RS components, digikey, farnell, mouser) seem to have such a product (in mass supply greater than quantities of 250) on a glance through their product catalogs.

The following crystals appear to meet the specs, but they may be close to end of line as their stocks are low...

http://uk.farnell.com/aker/c7s-24-000-12-3030-x/crystal-smd-ceramic-24-000mhz/dp/1538819

http://uk.farnell.com/aker/c6s-24-000-12-3030-x/crystal-smd-cer-24-000mhz/dp/1538833

Many Thanks 

Isn't there a capacitance of ~7pF at the Pin itself which gives about 20pF together with the 12pF capacitor? As such, you'll need a 20pF x-tal.

Bob

Oh of course!!!!!! Excuse my ignorance.  Many thanks for the clarification

Glad to have helped you!

Bob