If the power is cut, is the micro controller use battery power automatically?

[KKIM.6]

I'm developing STM32WB55VQ power system but I wonder the microcontroller automatically use battery power or not when Vdd is cut.

Is there anybody can explain this?

[waclawek.jan]

 

JW

[KKIM.6]

Can I use secondary battery for Vbat connection? if possible what happen when power is supplied by battery charger to battery?

[waclawek.jan]

What do you mean by secondary battery? An accumulator?

You can use accumulator for VBAT. In some STM32 (I did not check for WB) there's even a provision for trickle charging (a switchable resistor from VDD to VBAT).

If the charger does not exceed the maximum voltage for VBAT stated in the datasheet, it is OK.

JW

[Andrew Neil]

@KKIM.6​ - What "battery" are you talking about?

As @Community member​ showed, the chip has a dedicated "VBAT" power domain - is that what you're talking about?

Or are you talking about a battery to supply your entire system? In that case, the design is down to you - to make it work in whatever way you want/need it to.

[KKIM.6]

Secondary battery means Li-ion/polymer battery. In the embedded system. the battery will connected to the battery charger and the battery charger is continuously charging battery.

My question is whether the charging bias can affect to the microcontroller.

[Andrew Neil]

This is entirely down to your system design - it's up to you to design it to work the way you want/need it!

"whether the charging bias can affect to the microcontroller"

I don't understand what you mean by that.

The microcontroller neither knows nor cares what is supplying its power: it just needs to remain within the specified power supply limits - see the datasheet.

If you're asking about the charger's behaviour, then you need to refer to the charger documentation.

[Tesla DeLorean]

Well I suppose it means can it get upward of 4.2V, which would seem to exceed expectations. Where the nominal range is 1.55 to 3.7 V, and a max of 4V

Doesn't the SM32WB55 provide for battery charging on VBAT vs VDD internally?

One could presumably mux multiple supplies via diodes, but there are obviously considerations there too. A diode drop would afford you a little headroom on the upper voltage expectations at the IC.

Here's the Data Sheet, might be worth a review

https://www.st.com/resource/en/datasheet/stm32wb55rg.pdf

[KKIM.6]

Oh, I didn't know that the wb55 can charge battery.

However, it also arise a question on the recharging voltage.

Usually, the battery need 4.2 V to recharging but microcontroller only can generate 3.6 V maximum. is it fine?

[waclawek.jan]

VBAT pin supplies only RTC.

Read an answer Andrew's questions above.

There's no provision to switch between different VDD sources, and they must not exceed voltages given in DS. Design of VDD power source is entirely upon you.

JW​