Usage of decoupling capacitor in STM32H503KBU6

[bhavan_kumar]

Hi, 

     I am currently using STM32H503KBU6 MCU (32 pins). For my project the space in PCB board is critical. I have placed a LDO, Level translator, voltage supervisor and along with their associated passives in a 10mmx16mm PCB board. Now I still need to place three resistor, which I can't able to place because there is no space. My question is that is it necessary to use a high value decoupling capacitor (4.7uF) for VDD and VDDA? Because if I remove those two 4.7uF capacitor, I will get some space to place the three resistors. Kindly give me your thoughts about this. I have attached schematic images which is available in STM website.

Thanks,

Bhavan 

[Andrew Neil]

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@bhavan_kumar wrote:

I need to place three 0 ohms resistor for SWD debug interface

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Why does that need zero-ohm resistors?

:thinking_face:

[bhavan_kumar]

In order to do a SWD debug interface we need to connect the respective pin (PA13, PA14, NRST) to a 0 ohm resistor

[Andrew Neil]

But why zero-ohm resistors?

Why not just connect direct to your debug header/testpoints/whatever - especially as you're short of space?!

[bhavan_kumar]

Our MCU has been soldered on the PCB. So, we can't able to directly connect the debugger pin to the MCU. In order to connect the debugger pins we need to fan out the respective MCU pins using a 0 ohms resistors.

[Tesla DeLorean]

Ok, but not clear why this is the solution..

You could provide a debug header off board, ie part of the panel that's removed later., post programming

Or as edge castellations. 

[Andrew Neil]

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@bhavan_kumar wrote:

Our MCU has been soldered on the PCB. So, we can't able to directly connect the debugger pin to the MCU

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Sure you can:
 

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@bhavan_kumar wrote:

In order to connect the debugger pins we need to fan out the respective MCU pins using a 0 ohms resistors.

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You don't need zero-ohm resistors to do that.

Just place testpoints; eg,

Or solder fine wires directly: