Substituting crystal for ceramic resonator.

[Ian Stirling]

I'm considering substituting a crystal for a ceramic resonator in a
USB project (12Mhz).
I have a few of these to make, so using the 12Mhz crystals I already have
would be nice.
Is this possible simply by altering the capacitive loading?
Anything to watch out for?
As I understand it, this may overdrive the crystal. But I don't especially
care about frequency - 500ppm is fine, so is this an issue?
Many thanks.

 

[PeteS]

Are you trying to replace a resonator that the mfr expects to be on the
pins of the device?

Resonators and crystals have somewhat different operational modes, and
the on-chip oscillator may not work with a crystal. If you have the
details of the onboard oscillator (from the datasheet or perhaps in an
app note), I would run it by the group (perhaps on a.b.s.e).

I wanted to do this (on a USB hub device), but my crystal supplier
stated quite unequivocally that the onboard oscillator required a
ceramic resonator and they had no crystal that would work as is. By
altering the loading and perhaps providing a DC feedback path (100k or
so in parallel with the crystal) things *might* work, but it will
depend on the implementation details of the oscillator.

Cheers

PeteS

 

[Pooh Bear]

I'm considering substituting a crystal for a ceramic resonator in a
USB project (12Mhz).
I have a few of these to make, so using the 12Mhz crystals I already have
would be nice.
Is this possible simply by altering the capacitive loading?
Anything to watch out for?
As I understand it, this may overdrive the crystal. But I don't especially
care about frequency - 500ppm is fine, so is this an issue?
Many thanks.

What's the oscillator ?

Most chips will use resonators or crystals equally happily but the capacitive
loading may have to be altered ( see the crystal / resonator mfr's datasheet
and the semi makers too ).

Graham