RTC stops on LPC1768

Discussion created by lpcware Employee on Jun 15, 2016
Latest reply on Jun 15, 2016 by lpcware
Content originally posted in LPCWare by Karlsberg on Thu Sep 13 07:18:09 MST 2012
Dear Sir/Madam,

for the first time we use the RTC on the LPC1768 in a new product.

XTAL1 and XTAL2 pins are connected to a quartz crystal 32.768KHz.
Additionally each pin has one 22pF capacitor to ground.
Tuning Fork Crystal Specifications:
Series resistance: max. 40k Ohm 
Load capacitance: 12.5pF
A CR2032 lithium battery is used for alternative power supply for the RTC.

Unfortunately, the RTC often stops when the 3.3V main power supply was turned on.
Likewise, it is possible to "blow out the RTC", even without halitosis. ;-)

Replacing the quartz has not helped.
Does anyone have any idea what is wrong?
Is there a recommendation for the quartz?
What's about the parasitic capacitance of the chip?

Thank you for your trouble.

Yours faithfully,