Re: 32kHz crystal issues
- From: Rich Grise <rich@xxxxxxxxxxx>
- Date: Thu, 12 Jul 2007 16:57:19 GMT
On Thu, 12 Jul 2007 11:46:52 -0400, DJ Delorie wrote:
....
I'm mostly wanting to make sure the design will work on the PCB. That
boils down to three questions:
1. Am I calculating the load caps right? If the spec says "8pF" and
the crystal is 1pF, I need 7pF*2 = 14pF capacitors each?
When the spec says "8 pF", it means that the cap should have 8 pF in
parallel with it, including the capacitance of the input pins and
strays.
2. Is the 330k resistor the right value? How do I calculate the right
value for that specific crystal, given the OSC2 sine wave and 1uW
power?
That depends more on the chip than on the crystal - the crystal is
involved in that the R value probably sets the drive level, kind of like
a feedback resistor. If the spec says 330k, I'd start with that.
3. Are there other design issues I haven't mentioned, that I'd need to
be aware of when laying out the PCB? I know about the guard ring and
the keep outs, anything else?
As much ground plane as you can put on the board; billions and billions
of bypass caps. ;-)
Cheers!
Rich
.
- References:
- 32kHz crystal issues
- From: DJ Delorie
- Re: 32kHz crystal issues
- From: RST Engineering \(jw\)
- Re: 32kHz crystal issues
- From: DJ Delorie
- 32kHz crystal issues
- Prev by Date: Re: DTMF dead?
- Next by Date: Re: how to tell V and A of a pot
- Previous by thread: Re: 32kHz crystal issues
- Next by thread: Re: 32kHz crystal issues
- Index(es):
Relevant Pages
|
