Why should in 'G4 PB8/BOOT0 be set to non-Analog?

waclawek.jan · ‎2023-08-30

In 'G4 Datasheets and RM, the following remark can be read:

It is recommended to set PB8 to a different mode than the analog one to limit the
consumption that would occur if the pin is left unconnected.

This must be important, as it's at both in DS and RM, and in RM it's repeated twice (with slightly different wording).

But why?

Isn't Analog the low-power option?

PB8 doesn't even have an Analog functionality.

JW

Foued_KH · ‎2023-08-30

Hello @waclawek.jan ,

I will check this internally.

Foued

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waclawek.jan · ‎2023-08-30

Thanks, Foued.

Jan

Foued_KH · ‎2023-09-04

Hello @waclawek.jan ,

The PB8 pin has no analog switch and therefore cannot be set into analog mode.

There is need to change PB8 pin into mode which is safe regarding to consumption if it is left unconnected.

Foued

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waclawek.jan · ‎2023-09-04

Hi @Foued_KH ,

Sorry, but I don't quite get it.

Is PB8 the only pin which does not have analog switch?

And, would PB8 be set e.g. to Input, how would it be safer regarding to consumption, if left unconnected?

Thanks,

Jan

Foued_KH · ‎2023-09-04

If voltage on PB8-BOOT0 pin is in the middle of the VDD supply – even if PB8 is configured in analog mode - then there is higher consumption.
PB8 looks like configured in input mode instead of analog mode. This consumption can be caused by PB8 or by BOOT0 pin.
What does happen if BOOT0 signal is floating?
>>The consequence is that if the device is under reset and PB8 pin is floating then there is higher consumption.

Workaround is to configure PB8 in output mode or enable pull-up/down on it.

Foued

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waclawek.jan · ‎2023-09-04

Hi Foued,

I clicked on "Accept as solution" by mistake... that last post made me even more confused.

> Workaround is to configure PB8 in output mode or enable pull-up/down on it.

The multiple remarks in DS and RM don't state this.

>>The consequence is that if the device is under reset and PB8 pin is floating then there is higher consumption.
> Workaround is to configure PB8 in output mode or enable pull-up/down on it.

Under reset, how can I configure PB8 in output mode etc.?

Can you please quantify the "higher consumption"?

Thanks,

Jan

@Foued_KH