Pcb Layout Recommendations; Figure 29. Separating The Analog And Digital Layouts - ST STM32 Application Note

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3.2.12

PCB layout recommendations

Separating the analog and digital layouts
It is recommended to separate the analog and digital circuitry on the PCB (see
This also avoids tracks crossing each other. The tracks carrying digital signals may
introduce high-frequency noise in analog signals because of coupling.
The digital signals produce high-frequency noise because of fast switching.
Coupling of a capacitive nature is formed due to the metal connections (tracks) separated
by the dielectric provided by the PCB base (glass, ceramic or plastic).
It is recommended to use different planes for analog and digital grounds. If there is a lot of
analog circuitry then an analog ground plane is recommended. The analog ground must be
placed below the analog circuitry.
Separating the analog- and digital-circuit power supplies
It is desirable to have separate analog and digital power supplies in cases where there is a
lot of analog and digital circuits external to the microcontroller (see
on the STM32 package, different analog and digital power supply and ground pins are
available. The V
If you use a switching-type power supply for the digital circuitry, you should use a separate
linear supply for the analog circuit. Also, if you expect a lot of noise on the DC power supply
due to I/O switching etc., it is preferable to use a separate supply for the analog circuit.

Figure 29. Separating the analog and digital layouts

/V and V pins can be powered from separate power supplies.
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Figure 30). Depending
Figure 29).
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