Power battery domain with RTC only

Discussion related to "under the hood" OpenMV topics.
sys1up
Posts: 7
Joined: Sat Jun 09, 2018 3:41 pm

Power battery domain with RTC only

Postby sys1up » Thu Apr 18, 2019 4:16 am

Hello together,
I'm on the openmv M7. I like to keep the RTC of the stm32m7xx battery powered to retain the time if the openmv is in stop mode.

Acccording to the schematics VDD and VBAT are connected.
That means I will draw my battery if no other power supply is given.
That means I cannot power the battery domain in openmv m7 sepeately to keep RTC information while the openMV has no access to main power supply.
Is this correct?

Best regards!
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iabdalkader
Posts: 1141
Joined: Sun May 24, 2015 3:53 pm

Re: Power battery domain with RTC only

Postby iabdalkader » Thu Apr 18, 2019 1:12 pm

As long as you keep the power supply connected, the RTC will keep working in low power modes. And yes VDD and VBAT are connected.
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kwagyeman
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Joined: Sun May 24, 2015 2:10 pm

Re: Power battery domain with RTC only

Postby kwagyeman » Thu Apr 18, 2019 3:27 pm

Our board draws about 1mA in stop mode. Once H7 sales increase we may rev the board to give it more features. However, the amount of inventory we are moving will have to go up by an order of magnitude for that.
Nyamekye,
sys1up
Posts: 7
Joined: Sat Jun 09, 2018 3:41 pm

Re: Power battery domain with RTC only

Postby sys1up » Fri Apr 19, 2019 4:19 am

Thank you for your answers.
The application of seperating the battery power domain from VDD and exposing the VBAT pin would allow:

Keep the RTC going while openMV is stopped and waiting for external interrupt to continue working.

Due to the fact that the I2C does not have pullups usage of common external DS1307 modules with the OpenMV is not plug an play.

Best regards!
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kwagyeman
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Re: Power battery domain with RTC only

Postby kwagyeman » Fri Apr 19, 2019 11:15 am

I think you can turn pull ups built into the I/O pins on. Keep in mind the I2C bus can also be a UART or general I/O pin. It would have not made sense to add pull ups.
Nyamekye,
sys1up
Posts: 7
Joined: Sat Jun 09, 2018 3:41 pm

Re: Power battery domain with RTC only

Postby sys1up » Sat Apr 20, 2019 5:11 am

You are right!...

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