2412402_en-US

[#1]

PCF2131 or PCA2131 with a supercapacitor

Hello 

I have few question regarding the RTC PCF2131 or PCA2131, especially when used with a supercapacitor.

1- I haven't seen in the components internal scheme a charging path for the energy tank.

     Can you confirm that I must plan for a charging path externally  ( a diode to make it simple ) ?

2- Would it be possible to have VBAT > VDD ?

3. When used with a supercapacitor, charged to the ~ the same voltage as VDD :

   What is the recommended register setting ?

Thank you.

Nicolas

Re: PCF2131 or PCA2131 with a supercapacitor

Hello RafaR.

Thanks for the answers.

Have a good day.

BR,

Nicolas

Re: PCF2131 or PCA2131 with a supercapacitor

Hello nicolas75

Good day!

1.- Yes. The PCF2131/PCA2131 contains only an internal switch-over circuit (a comparator/switch block between VDD and VBAT) — there is no internal charging path for VBAT. The device simply monitors VDD and switches to VBAT when a power failure condition is detected; it does not charge whatever energy source is on VBAT.

2.- Yes, it’s possible, but the device can only start up from VDD. Applying only VBAT without first powering VDD will not start the RTC.

3.- PWRMNG[2:0] = 000

The datasheet specifically warns:

Direct switching mode is not recommended if VDD and VBAT are similar (for example VDD = 3.3 V and VBAT ≥ 3.0 V).

Since your supercapacitor is charged to approximately the same voltage as VDD, Standard Mode is the recommended configuration.

I hope this information has helped you, please let me know if you need help with anything else.

Have a great day and best of luck.