Fujitsu F2MC-16LX Series Application Note page 8

For 2-layer boards should be used a closed ground plane (located directly below the MCU).
The Vcc supplies should be taken from the bottom layer.
For 4-layer boards should be used the inside layers for GND and Vcc supplies. In this case,
both layers form additional capacitor (broadband behaviour) for the power supply.
Figure 8 shows an example of a star connection for Vcc supplies on the MCU.
This method of Vcc connection reduces the loop of the Vcc lines around the MCU, thus
reducing noise emission. A variation of this circuit may be needed, if separate filtered supply
voltages are routed to the A/D supplies (pin 34/37).
Connection to
power supply
ground plan
below package
on the top side
Vss
Decoupling capacitor C on
B
the back side of the PCB
Decoupling capacitor C on
B
Vcc
the back side of the PCB
VCC3C
Figure 8: 16LX family with a subclock or stepper motor driver,
recommended layout for multiple layers PCB
Note: All decoupling capacitors on the Vcc pins should have the same value.
These capacitors should be placed close to the Vcc pin. The Vcc/Vss current should flows
through the pad of the capacitor.
star point and noise
filter for
Vcc and ground Via to MCU supply
on the back side
C
B
C
B
Decoupling capacitor C on
B
the back side of the PCB
ground plane
on top and
botton layer
Q
C
C
Q
X0A
C
B
X1A
Via to ground island
and system ground
HVss
HVcc
Decoupling capacitor C
HVss
the back side of the PCB
HVcc
HVss
Single ground island
on the back side
on
B
8