[SI-LIST] Re: follow up: Re: Query about Oscillator problem
- From: Richard Jungert <r_jungert@xxxxxxxxxxx>
- To: steve weir <weirsi@xxxxxxxxxx>, <tlx6f@xxxxxxx>, <chundis@xxxxxxxxx>, si list freelist <si-list@xxxxxxxxxxxxx>
- Date: Mon, 1 Feb 2010 13:49:20 -0800
Guys
It may very well be that the series resonant quartz won't work and that you may
need to get a parallel resonant XTAL. Series resonant can get you into trouble.
I would go with the crystal type/mfg that Motorola recommends.
I would bet dollars to doughnuts that the resonant type is the issue here.
Richard Jungert
> Date: Sun, 31 Jan 2010 15:20:46 -0800
> From: weirsi@xxxxxxxxxx
> To: tlx6f@xxxxxxx
> CC: chundis@xxxxxxxxx; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: follow up: Re: Query about Oscillator problem
>
> Li, that is not correct. NPO capacitors are high stability and high Q.
> They are great for the crystal tuning caps where both characteristics
> are a plus. But the high Q can actually create unwanted resonance
> problems in the PLL power filter.
>
> Steve.
> Li, Tianqi . (S&T-Student) wrote:
> > Sree,
> >
> > I forget sth. You need to check the PLL filtering capacitors of MCF5212.
> > In most cases CPU will leave out 2 or 3 power pins for filtering PLL
> > noise. Capacitors on these pins should also use NPO for a better
> > performance.
> >
> > And you also need to find at what value of Vpp of XTAL droped to the PLL
> > start to lose locking. If the value is out of MCF5212 spec, the root
> > cause is surely on XTAL tank circuit; If not, it might be XTAL's glitch
> > aroused. You can use scope to test the eye diagram and find the glitch.
> >
> > Tianqi Li
> >
> > -----Original Message-----
> > From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> > On Behalf Of Li, Tianqi . (S&T-Student)
> > Sent: Sunday, January 31, 2010 4:44 PM
> > To: chundi srikanth; si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] Re: Query about Oscillator problem
> >
> > Hi Sree,
> >
> > 1) I think you should check the tuning capacitors temp. grade first. In
> > this case you need to use NPO grade. If you are using Y5V, it won't work
> > well when temp. changes a lot.
> >
> > 2) Make sure that the tuning capacitor's value is same as what
> > recommended in MCF5212 app. Notes.
> >
> > 3) If capacitors are OK, you need to check XTAL power consumption and
> > make sure that MCF5212 can drive the XTAL at low temp.
> >
> >
> > Tianqi Li
> >
> > -----Original Message-----
> > From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> > On Behalf Of chundi srikanth
> > Sent: Saturday, January 30, 2010 10:18 AM
> > To: si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] Query about Oscillator problem
> >
> > Hi Friends,
> > I have designed a board with MCF5212 Processor and it was interfaced to
> > a
> > Pericom (saronix-ecera) NKS5 series quartz crystal. The crystals
> > operating
> > temperature was -40Deg c to 85Deg c. Earlier i tested this board and
> > everything was fine but now because the PLL was not locking and
> > processor
> > was working. So when i observed i noticed that at ambient temperature
> > the
> > crystal clock output was 2V p-p but with decrease in temperature the
> > clock
> > output was decreasing below 0.8V at -40 Deg c.
> >
> > Can you just give me an idea about this problem and what might be the
> > problem in this scenario?
> >
> > Thanks & Regards
> > Sree
> >
> >
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> --
> Steve Weir
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