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Francisco SinapseEnergia
Francisco SinapseEnergia
Associate III
May 11, 2018
Question

STM32F215 VBAT pin

  • May 11, 2018
  • 1 reply
  • 1794 views
Posted on May 11, 2018 at 13:28

Hi all, I'm using a STM32F215 MCU with a supercapacitor (like XH414HG-IV01E;SEIKO) connected to Vbat through a 0 Ohm resistor in order to backup RTC registers. I attach an image:

0690X0000060B1AQAU.png

Well. If I measure the voltage in VBAT pin, it shows 0.18V. If I remove the 0 Ohm resistor, VBAT pin measure 1.18V.

My doubts are:

1. How exactly VBAT pins works?

2. VBAT pins charge the supercapacitor itself?

3. Should I control VBATE register to charge the supercapacitor? 

4. Does my schematic wrong?

Thanks in advance.

    This topic has been closed for replies.

    1 reply

    kajtek610
    kajtek610
    Associate II
    May 11, 2018
    Posted on May 11, 2018 at 15:18

    Hi!

    I'm not sure why you add an extra resistor between Vbat and Vcc. Low drop schottky diode would be better.  If there is power supply, supercap is charging through resistor (let's say 22 ohm) and Vbat is supply from Vcc. When voltage drop to 0 on Vcc, supercap do the job to keep RTC alive through Vbat.

    You also have to enable the PWR clock interface, and access to the backup domain if needed in software, check out example projects.
    Francisco SinapseEnergia
    Francisco SinapseEnergiaAuthor
    Associate III
    May 11, 2018
    Posted on May 11, 2018 at 16:39

    Thanks for your reply. I will check my design.

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