STM32F215 VBAT pin

[Francisco SinapseEnergia]

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:

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.

[kajtek610]

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]

Posted on May 11, 2018 at 16:39

Thanks for your reply. I will check my design.