topic Re: Regarding Battery back-up (VBAT) used in MK70FN1M0VMJ12 for RTC in Kinetis Microcontrollers

Regarding Battery back-up (VBAT) used in MK70FN1M0VMJ12 for RTC

puspamnayak — Fri, 22 Aug 2014 06:29:03 GMT

Hi,

I want to know do i need external logic circuit (OR circuitry) while switching from VDD to VBAT
(coin cell battery for RTC) and vice versa or

switching will happen internally between VDD to VBAT and VBAT to VDD depending on detection of
supply voltage VDD by internal logic in MK70FN1M0VMJ12

Kindly reply at earliest

Thanks and regards,

Puspam N

Re: Regarding Battery back-up (VBAT) used in MK70FN1M0VMJ12 for RTC

egoodii — Fri, 22 Aug 2014 11:37:34 GMT

Achieved externally with a dual-schottky-diode device like BAT54C.

Re: Regarding Battery back-up (VBAT) used in MK70FN1M0VMJ12 for RTC

puspamnayak — Fri, 29 Aug 2014 04:41:25 GMT

Thanks Earl. Information will help...

Thanks once again

Regards,

Puspam N

Re: Regarding Battery back-up (VBAT) used in MK70FN1M0VMJ12 for RTC

egoodii — Fri, 29 Aug 2014 14:44:25 GMT

Re: Regarding Battery back-up (VBAT) used in MK70FN1M0VMJ12 for RTC

puspamnayak — Mon, 01 Sep 2014 09:24:38 GMT

Hi Earl,

Thanks for giving this valuable information and for sharing schematic for VBAT hardware connection.

I have a question on this, i am using two K70 micrcontroller on my board. One K70 will have RTC battery back-up using Coin cell and for other K70 we dont need power for RTC so in that case can i keep VBAT pin open or that has to be terminated to ground.

Kindly suggest on this query

Thanks and Regards,

Puspam N

Re: Regarding Battery back-up (VBAT) used in MK70FN1M0VMJ12 for RTC

adriancano — Mon, 01 Sep 2014 15:52:19 GMT

Hi,

If you are not planning to use the RTC module then you can leave the VBAT pin floating; try to never access to the RTC registers to avoid bus faults and also the RTC clock gate in the SIM register should it remains in value 0.

Hope this information can help you.

Regards,

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Re: Regarding Battery back-up (VBAT) used in MK70FN1M0VMJ12 for RTC

puspamnayak — Tue, 02 Sep 2014 04:22:48 GMT

Hi Adrian,

Thanks for the clarification. This information will definitely going to help for the projects using freescale microcontroller.

Best and Warm Regards

Puspam Nayak