[SI-LIST] Re: follow up: Re: Query about Oscillator problem
- From: steve weir <weirsi@xxxxxxxxxx>
- To: "Li, Tianqi . (S&T-Student)" <tlx6f@xxxxxxx>
- Date: Sun, 31 Jan 2010 15:20:46 -0800
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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