Crystal Oscillator; Power Supply Decoupling; Figure 22. Six Layer Pcb Stack-Up Example - ST STM32F4 Series Application Note

AN4488
8.2

Crystal oscillator

Use the application note: Oscillator design guide for STM8S, STM8A and STM32
microcontrollers (AN2867), for further guidance on how to layout and route crystal oscillator
circuits.
8.3

Power supply 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 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 filtering Ceramic capacitors
(100 nF) and one single Tantalum or Ceramic capacitor (min. 4.7 µF typ.10 µF) connected in
parallel. 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. Figure 22 shows the typical layout of such a
VDD/VSS pair.
Recommended PCB routing guidelines for STM32F4xxxx devices

Figure 22. Six layer PCB stack-up example

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