LPC176x RTC crystal and capacitor recommendations

[lpcware]

Content originally posted in LPCWare by parikshitkr on Wed Dec 12 04:32:58 MST 2012
Hi,

In LPC1768 datasheet (rev 9) I see in section 14.2 guidelines on Crystal and load capacitor. For RTC I can not find a clear guideline on what crystal to use and load capacitor for it. Could you recommend should be crystal specs, i.e., something similar to Table 22.

regards
Parikshit

[lpcware]

Content originally posted in LPCWare by Daniel Widyanto on Wed Dec 19 00:31:00 MST 2012
Hi,

The RTC oscillator recommended 32kHz crystal to have:
- CL (Crystal Cap load): 11pf, Max Rs (Crystal series resistance) < 100kohm, Recommended external cap: 18pF (or)
- CL (Crystal Cap load): 13pf, Max Rs (Crystal series resistance) < 100kohm, Recommended external cap: 22pF (or)
- CL (Crystal Cap load): 15pf, Max Rs (Crystal series resistance) < 100kohm, Recommended external cap: 27pF

We'll feedback your input for the RTC xtal selection into User Manual. Thanks for bringing this up