SV: SV: [Icc-avr] 32 KHz Crystal start up problems

Tue Jan 29 14:44:47 PST 2008

I came along megaXX8p datasheet today, and found LF crystal load cap discussed on page 33:

http://www.atmel.com/dyn/resources/prod_documents/doc8025.pdf

As megaXXX0/1 are same chip generation as picopower parts, they can be assumed to behave alike.

Best regards,
Johannes

> Thanks Dan! This type of information you give is very useful to us to.

> /Bengt

>   _____

> Från: icc-avr-bounces at imagecraft.com [mailto:icc-avr-bounces at imagecraft.com]
> För Dan Mullin
> Skickat: den 23 januari 2008 18:51
> Till: Discussion list for ICCAVR and ICCtiny Users. You do NOT need
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> Ämne: Re: SV: [Icc-avr] 32 KHz Crystal start up problems

> Another thought, Patrick,

> I don't know if this is in a production environment but take a look at any
> flux residue or contamination possibly left on the board. We had a serious
> problem a number of years ago where some water-soluble flux residue was not
> being properly cleaned off the PCB's. In our very dry Colorado environment
> the PCB would test out fine but, once the unit was powered up in a location
> with high humidity, the flux would actually absorb moisture out of the air
> and alter the capacitance on and around the crystal, causing the circuit to
> not start. This was tough to find but, once we made the connection, all of
> the problems instantly went away and have never returned!

> Good luck,

> Dan Mullin

> Bengt Ragnemalm wrote:

> The lower load crystal solution was interesting. As for all crystal you
> should always read the spec careful to find out the load capacitance as
> stated in the datasheet for the crystal, not the microcontroller. Questions
> about load capacitance is very common although you may be aware of it and
> still have problems. But if the crystal starts if you touch it with the
> probe, it sounds to me that you need more load capacitance. Touching with
> fingers is not so informative as it may often lead to resistive and huge
> capacitive load to other sources than ground.

> /Bengt

> -----Ursprungligt meddelande-----
> Från: icc-avr-bounces at imagecraft.com [mailto:icc-avr-
> bounces at imagecraft.com] För Johannes Assenbaum
> Skickat: den 17 januari 2008 20:24
> Till: icc-avr at imagecraft.com
> Ämne: Re: [Icc-avr] 32 KHz Crystal start up problems

> Hi Patrick,

> at work we have a customer series production that at the start had similar
> problem with 32kHz crystal, connected to an ADC in this case. Solution was
> a crystal with lower load cap specified.

> hth,

> Johannes

> Hope this finds you all well.

> I'm just wondering if anyone has had problems with the 32KHx crystal not
> starting up on the Atmel processors.

> I've use them many times before and never had a problem, but on this

> latest

> project they quite often don't seem to start up. I have to touch one of

> the

> legs with a probe etc.. Then they run fine.

> I'm using the mega1280, 3.3Volts.

> I've had problems a long time ago (PACS days Andy) with the wrong

> crystal

> capacitance on a very low power RTCC, but did not thing the AVRs were

> that

> sensitive. I've just used a watch crystal from Farnell.

> Thanks in advance for any suggestions,

> Patrick

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