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Crystal oscillator doesn't work on P89LPC936

Started by pyalpc936 July 18, 2007
Hi,
I'm using a P89LPC936 with a 12MHz crystal (SMD case HC49/4H)
The uC doesn't always start.
It seems that oscillation level is too small (0.5V to 1.6V with 3.3V
Vdd).
Also it seems to work fine with a classic crystal (not SMD).
The reason could be that classic crystal have serie resistance (about
10 ohms) much lower then SMD crystal (about 30 ohms). And the 89LPC936
doesn't have enough gain to compensate the lost due du serial
resistance.
I don't find any information about crystal to use with LPC9XX
microcontroler.

Does anyone have informations or perhaps similar problems ?

Thanks a lot
Hi,
There seems to be an issue with startup on some types of crystals.
NXP put out an app note:

http://www.standardics.nxp.com/support/documents/microcontrollers/pdf/an10289.pdf

Hope it helps.

Jeff

--- In l..., "pyalpc936" wrote:
>
> Hi,
> I'm using a P89LPC936 with a 12MHz crystal (SMD case HC49/4H)
> The uC doesn't always start.
> It seems that oscillation level is too small (0.5V to 1.6V with 3.3V
> Vdd).
> Also it seems to work fine with a classic crystal (not SMD).
> The reason could be that classic crystal have serie resistance (about
> 10 ohms) much lower then SMD crystal (about 30 ohms). And the 89LPC936
> doesn't have enough gain to compensate the lost due du serial
> resistance.
> I don't find any information about crystal to use with LPC9XX
> microcontroler.
>
> Does anyone have informations or perhaps similar problems ?
>
> Thanks a lot
>