Battery/Supercap backed RTC

[QumJo]

Hi

I would like to have an RTC keep-alive when main power is down using a Supercap or Battery (I do not supply V_BATT as the default application is PoE).

Can I somehow supply the RTC from an external source (thinking of an 3.5V supercap that can bridge suppl for a few days) or is it safest if I use an additional RTC on my board (e.g. MCP79411T-I/SN) to have said feature?

I am using an SiT1532 as RTC oscillator, powered from the battery/supercap. Can I split the output of this oscillator and feed it both to the additional RTC X1_IN and the OSC1_IN pin? If so, how to go about the OSC1_GND? leave floating?
Or is it better to just use the external RTC? How then to correctly disable the internal RTC such that the device still boots?

Thanks!

[Eshtaartha Basu]

Hello QumJo,

You can find the recommendations for your question here (https://octavosystems.com/forums/topic/rtc-circuitry/#post-10010). The RTC recommendations for OSD335x BAS apply to C-SiP as well.

You can find more useful discussions on RTC circuitry of OSD335x family under this topic (https://octavosystems.com/forums/topic/rtc-circuitry/)

Hope this helps.

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