AN2014 datasheet(36/65 Pages) STMICROELECTRONICS

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Hardware considerations

AN2014

36/65

DocID10701 Rev 10

4.4

PCB Layout considerations

The full system layout becomes ever more critical because of space constraints, high

communication speed, noise due to interference and all EMC constraints.

4.4.1

Cross coupling

The cross coupling effect increases with the frequency and fine PCB technology. All floating

signals or pins, weak pull-up or pull-down connections are very sensitive to cross coupling

and antenna-like pick-up. All unused pins should be tied correctly (in general to VCC or VSS).

4.4.2

Noise and disturbances on power supply lines

Noise and disturbances on power supply lines must be filtered out. For a robust design it is

recommended to place local decoupling capacitors. Low inductance capacitors in the range

of 10nF to 100nF are usually preferred.

Electrolytic capacitors in the range of 1 µF to 100 µF can also be placed close to the power

supply source of the system. Avoid Ground and VCC loops on the PCB as it increases the

sensitivity to electromagnetic fields. (See Figure 32: PCB decoupling.)

Figure 32. PCB decoupling

AN2014 Datasheet(PDF) 36 Page - STMicroelectronics