STM32L452RET6 Question

[iHamd.1]

Hi all,

I am using the STM32L452RET6 On my board and i have 2 quiestion regarding it:

1) VDD12 Net - how to set my hardware when i am not using external DC/DC? floating? GND? just a cap? if so what size?

2) when entering boot mode and going over the i/o voltage i noticed a few anomalies -

a) some USART legs were 3.3V and some not (USART1 both 0V, USART2 only one is 3.3V and USART3 Both were 3.3V) - why is that?

b) PA0 GPIO is 3.3V for some reason - why is that? couldn't find a purpose on datasheet.

Thanks in advance,

Ido

[waclawek.jan]

Note, that there are two different versions of STM32L452RET6 - VDD12 pin is present only on models with external SMPS, i.e. with P suffix.

Pins in bootloader may have enabled internal pullups/pulldowns, see AN2606.

JW

[iHamd.1]

its the STM32L452RET6P vresion.

If External SMPS is not required, What do i do with it?

[Amel NASRI]

Hi @iHamd.1​ ,

I suggest you refer to the following application notes:

• AN4555: Getting started with STM32L4 Series and STM32L4+ Series hardware development
• AN4978: Design recommendations for STM32L4xxxx with external SMPS, for ultra-low-power applications with high performance

-Amel

[iHamd.1]

Hi Amel,

Thank you for your suggestion.

I already went through these applications...

In AN4978 it says: From these sentences, can i assume that if i leave VDD12 with NO EXT SMPS AT ALL it is okay since the internal LDO will supply the internal logic?

Also, what do i do with these pins? i examined the STM32L452RETP NUCLEO Evaluation board and saw 2 1nF caps for the VDD12 pins.

So what do i do with the VDD12 Pins if i do not use ANY EXT SMPS?:

1) Leave floating

2) Connect a cap to GND.

Thanks in advance,

Ido

[M4R10]

Hello,

here I have the same question about VDD12, leave floating or connect a cap to GND?

Can somebody says what we should do with this?

thanks

[Piranha]

From AN4555.

Section 2.1 Power supplies:

VDD12 ... It does not need any external capacitance and cannot drive an external load.

Section 2.2 Power supply schemes:

As these VDD12 pin are also connected to internal regulators, they cannot accommodate a decoupling capacitance, neither can they be shared with an external circuitry for other purposes.

Figure 3. Power supply scheme: no components connected to VDD12.