How should I go about following a MCU's Datasheet?

[Sashvat]

Hi everyone, I have been designing some circuits which have a microcontroller in them, I looked at a few people on YouTube designing microcontroller development boards, and they either put something thats additional, or they don't add something that is specified in the Datasheet. I am someone who is somewhat an intermediate in electronics, but when I look at the Datasheet power supply scheme, its different from what they do it. I am getting very confused about this. I don't wish to go too in-depth, but should I just stick to what they have asked in the schematic and go ahead? Thank you!

 

[Nigel Goodwin]

Will you give pretty well zero information - post some examples, and specify what uC you're using.

PIC's need VERY, VERY little in the power supply department, depending what you're doing with it, and what you're feeding it from.

 

[Sashvat]

Hi Nigel Goodwin, I use a STM uC, specifically a STM32F405RGT6, STM32F103C8T6, STM32L432KBU6, and many other uC's which I have kept aside based on my prototype tests. But when I see a tutorial, one in specific says, a 10uF cap needs to be placed in parallel with all the other decoupling caps for the uC, he says (In the video) that STM says its specified, but I have searched the Datasheet and its no where to be found. The other one is, VBAT is a pin in the uC, the Datasheet says you dont need a cap, but in the video he adds an extra one.

If you take a look at the screenshot below, the VBAT (highlighted in red) doesn't specify using a cap, nor do the points below (highlighted in orange) say that a capacitor needs to be placed near VBAT. The decoupling caps (highlighted in blue) don't specify the use of a 10uF cap nor do the points (in orange also state). I have also placed the schematic below for you to see what the video has told me to do. I have highlighted the respective one's in their colour for you to check what I have a question in.

 

[Nigel Goodwin]

It's usually good practice to add something like a 10uF across the supply rail, if it's actually 'needed' or not is a different matter.

If the datasheet doesn't specify them, then it's up to your personal choice if you fit them or not.

If you look up the 'Blue Pill' schematic, you'll see what that uses - and as a VERY low cost unit from China I presume it uses nothing it doesn't have to.

Personally, in my PIC projects, I simply use a 1uF multi-layer ceramic across the supply near the PIC, as well as on the in and out of the regulator.

 

[Sashvat]

Thanks a lot! And what about the 100nF attached to the VBAT pin? Is that also a safety measure for filtering? So in the future, when I am looking at a very different Datasheet (I will stick to STM) can I just blindly follow the required caps and components required?

 

[Nigel Goodwin]

Thanks a lot! And what about the 100nF attached to the VBAT pin? Is that also a safety measure for filtering? So in the future, when I am looking at a very different Datasheet (I will stick to STM) can I just blindly follow the required caps and components required?

If in doubt, try things both ways, a datasheet isn't a 'rule' - it's usually just the absolute minimum to make the component work, adding further capacitors could easily improve performance, such as lower noise levels on the A2D.

 

[Sashvat]

Thanks a lot!