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re.wolff9
re.wolff9
Senior
April 11, 2018
Question

Can I leave VBAT unconnected?

  • April 11, 2018
  • 11 replies
  • 8860 views
Posted on April 11, 2018 at 14:03

Hi, 

I Have a project that can be populated with or without RTC and a battery. Can I leave the VBAT pin unconnected when building PCBs without the battery?

I'm using an STM32F072. 

#stm32f0 #stm32 #vbat
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11 replies

waclawek.jan
waclawek.jan
Super User
April 11, 2018
Posted on April 11, 2018 at 17:53

If no battery, both RM0091 and AN4080 recommend to connect it to VDD.

JW

re.wolff9
re.wolff9Author
Senior
April 11, 2018
Posted on April 11, 2018 at 20:08

Well, yes. You're right. But I was hoping I would not need extra components when I don't mount the battery. Or what if I do mount the battery-holder, but the user forgets to replace the battery when it's empty? That creates a very similar situation as what I have now: Simply a floating VBAT. 

I just checked the 'decoupling your STM32F0xx' section in the datasheet. No capacitor on VBAT. And then RM0091 says to install a capacitor when connecting to VDD...  

waclawek.jan
waclawek.jan
Super User
April 11, 2018
Posted on April 11, 2018 at 21:28

I guess you can leave it unconnected as long as you don't use the RTC and other VBAT-related features.

Note that I am not ST so do this on your own risk.

JW

T J
T J
Senior III
April 11, 2018
Posted on April 12, 2018 at 00:12

use a jumper or solder blob under the battery itself.

if the battery is not installed, you must solder the blob , shorting out the Vbat to VDD

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