ADD backup battery to STM32F746 DISCO

[egywell]

Posted on October 30, 2017 at 17:19

HELLO

I want to connect backup battery to STM32F746 DISCO but from datasheet I see VBAT is connected directly to VDD 

is there any way to solve this problem ??

[LMI2]

Posted on October 30, 2017 at 20:48

746 CPU is a large chip, 208 pads, I think, and the board is a multilayer PCB. I bet you can't connect a battery to Vbat.

There are cheap RTC boards available on the net. I am not a salesman, so I wont give you any names but Google does.

[egywell]

Posted on October 31, 2017 at 07:36

thanks for reply

Why I have to connect external rtc board if cpu has very good rtc inside

they have to think about that 

the Disco board can be used very easy as final product after programmed so it should include this important feature

[LMI2]

Posted on October 31, 2017 at 17:51

'the Disco board can be used very easy as final product after programmed so it should include this important feature'

True. I think many demo boards from ST have Vbat connected to the VCC.

[john doe]

Posted on November 01, 2017 at 00:23

so the power supply options listed in the user manual don't help?

http://www.st.com/resource/en/user_manual/dm00190424.pdf

 

[Tesla DeLorean]

Posted on November 01, 2017 at 00:41

Not really, the OP is trying to separate the supplies so VBAT can be powered independently, with a battery.

At the moment the C1 ball connects to VDD plane, not sure if a trace is exposed in a usable fashion.

[Andrew Neil]

Posted on November 01, 2017 at 01:09

elbeshlawy.mohammed wrote:

Disco board can be used very easy as final product

You didn't read the licence agreement, then?

[egywell]

Posted on November 01, 2017 at 08:00

who read like that useless messages

[egywell]

Posted on November 01, 2017 at 08:02

RTC is useless  i have to re setup time each time  when power off

[roland van straten]

Posted on November 02, 2017 at 09:47

The board on itself is not very 'battery' friendly. A shortcoming of a lot of boards not being designed to use this kind of battery backup feature. You can start by disabling all peripherals and such to measure the power consumed on the 3.3V rail. Then you can decide to hook up a battery at 3.3V, with a diode is series. Not a beautiful solution, but it might work for you. If only the RTC is needed, using an external RTC with CR2032 battery would do the trick. You can buy this dirt cheap like the ones that are available for Raspberry Pi's (another design lacking a RTC). Using VDD as feeding point instead of 3.3V doesn't look good.

Regards,

R