RTC problems with LPC4330

[lpcware]

Content originally posted in LPCWare by midas on Thu Dec 19 17:07:04 MST 2013
I use a proprietary board based on the LPC4330. I have a 32768Hz crystal connected between RTCX1 and RTCX2, with 18pF capacitors to ground (as recommended in the Data Sheet, 13.3) at short distance from the micro-controller, and a 3V battery connected to Vbat. The battery backed RAM works (maintains content when power removed and restored). However, the RTC oscillator never starts oscillating, and when I try to debug any application that initializes the RTC, the debugger looses connection with the board in Chip_RTC_CalibCounterCmd(), after writing to register CCR ("terminating due to loss of debug control"). I have tried many variations of the RTC initialization code, with added delays inserted - to no avail.
Any ideas?.

[lpcware]

Content originally posted in LPCWare by midas on Thu Jul 16 04:33:31 MST 2015
Hi Michele,

Yes the higher current consumption of the RTC is a known problem, see latest errata, page 30. Errata

[lpcware]

Content originally posted in LPCWare by michele sponchiado on Thu Jul 16 00:38:50 MST 2015
Hi, thanks for your reply.
In my case, it was a wrong capacitor value which won't start the RTC oscillating.
We replaced both capacitors and the RTC now works fine.
The strange thing is that if the RTC clock won't work, and you enable the RTC, this hangs the whole chip!
Furthermore, we're experiencing a 9microAmpères current consumption from the battery (RTC_ALARM and SAMPLE pins are configured inactive as per errata sheet), while we were expecting about 4microA, so I'll post another question about this in the forum...

[lpcware]

Content originally posted in LPCWare by midas on Tue Jul 14 04:24:16 MST 2015
Hi Michele,

Yes, I have solved my problem eventually, by replacing the crystal I used from the FOX FSRLF327 to Abracon's ABS25-32.768KHz-4-T. Comparing the spec of both crystals, I can't say I notice any significant difference, so the margin for starting oscillating is possibly small, but it made all the difference between working and not working.

Regards

[lpcware]

Content originally posted in LPCWare by michele sponchiado on Tue Jul 14 01:56:36 MST 2015
Hi Midas,
I wonder if you solved your problem: I am facing the very exact problem right now.
Was it a PCB or capacitors problem?
Many thanks