STM32F4DISCOVERY VBAT pin

[ppsilv]

Posted on March 31, 2014 at 17:10

Hi all,

I want to use RTC from STM32F4DISCOVERY and have a doubt about VBAT pin that is connected to VDD through R26 0Ohm, this are saying that I need to take off R26 to plug a vbat battery, but if I take off the R26 a jerry-rig is needed to connect battery. So I ask, is it true, that I need to take off R26 and make a jerry-rig to plug vbat battery. or I can plug the vbat battery in VDD with a diode, because the cpu turn-off everything other peripherals, except VBAT domain , when VDD fall down below some value prefixed? Best regards, Paulo #rtc-vbat

[ppsilv]

Posted on April 01, 2014 at 14:06

Hi,

Is it a fool question?? I think that a lot of guys are using RTC in this kit. Nor Clive put an answer. Best regards. Paulo

[waclawek.jan]

Posted on April 01, 2014 at 14:25

> So I ask, is it true, that I need to take off R26 and make a jerry-rig to plug vbat battery.

For the purpose of running the RTC (and/or the battery-backup SRAM), yes. The F4 DISCOVERY kit is not well prepared for connecting a battery. > or I can plug the vbat battery in VDD with a diode, because the cpu turn-off everything other peripherals, except VBAT domain , when VDD fall down below some value prefixed? That is possible, but it would be a different setup, keeping the whole F4 under power, relying on it to power down its peripherals and go to some of the power-saving  modes (and resulting in higher consumption than in the previous case). On the DISCOVERY board, however, the other on-board ICs would remain powered by the battery, too. JW

[ppsilv]

Posted on April 01, 2014 at 16:30

Thank you so much for your answer.

\pdsilva

[Tesla DeLorean]

Posted on April 01, 2014 at 17:13

Nor Clive put an answer.

Perhaps the topic just didn't really interest me, or was framed awkwardly? Forum etiquette normally dictates if you don't have anything to add, don't post. And I didn't. I'm not sure removing or soldering parts on a cheap dev board represents ''jerry-rigging'', you're provided with a schematic for the express purpose of reviewing how the circuit works, and what you might be able to change on it. There is a lot of junk on the STM32F4-DISCO, the STM32L-DISCO might be a better choice, it has a provision for a battery, and has an LSE crystal mounted.

[waclawek.jan]

Posted on April 02, 2014 at 08:38

> There is a lot of junk on the STM32F4-DISCO

Well, I wouldn't call the missing provisions for battery connection ''junk'', but you probably had also other things in mind - could you please comment? Thanks, Jan

[ppsilv]

Posted on April 03, 2014 at 01:47

Thank you for the advice, but I am a simple developer, and the customer want use this board, it is cheap and easy to buy.

thank you.