Recommendations; Printed Circuit Board; Component Position; Ground And Power Supply (Vss , Vdd , Vdda ) - ST STM32F0 Series Application Note

AN4080
6

Recommendations

6.1

Printed circuit board

For technical reasons, it is best to use a multilayer printed circuit board (PCB) with a
separate layer dedicated to ground (V
provides good decoupling and a good shielding effect. For many applications, economical
reasons prohibit the use of this type of board. In this case, the major requirement is to
ensure a good structure for ground and for the power supply.
6.2

Component position

A preliminary layout of the PCB must make separate circuits:
●
High-current circuits
● Low-voltage circuits
●
Digital component circuits
● Circuits separated according to their EMI contribution. This will reduce cross-coupling
on the PCB that introduces noise.
6.3 Ground and power supply (V
Every block (noisy, low-level sensitive, digital, etc.) should be grounded individually and all
ground returns should be to a single point. Loops must be avoided or have a minimum area.
In order to improve analog performance, you must use separate supply sources for V
V , and place the decoupling capacitors as close as possible to the device. The power
DDA
supplies should be implemented close to the ground line to minimize the area of the
supplies loop. This is due to the fact that the supply loop acts as an antenna, and is
therefore the main transmitter and receiver of EMI. All component-free PCB areas must be
filled with additional grounding to create a kind of shielding (especially when using single-
layer PCBs).
6.4

Decoupling

All power supply and ground pins must be properly connected to the power supplies. These
connections, including pads, tracks and vias should have as low an impedance as possible.
This is typically achieved with thick track widths and, preferably, the use of dedicated power
supply planes in multilayer PCBs.
In addition, each power supply pair should be decoupled with 100nF filtering ceramic
capacitor and a chemical capacitor of about 4.7 µF connected between the supply pins of
the STM32F0xxx device. These capacitors need to be placed as close as possible to, or
below, the appropriate pins on the underside of the PCB. Typical values are 10 nF to 100 nF,
but exact values depend on the application needs.
such a V /V pair.
DD SS
Doc ID 023035 Rev 2
) and another dedicated to the V
SS
, V , V
SS DD DDA
Figure 12
Recommendations
supply. This
DD
)
shows the typical layout of
and
DD
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