AN2127 Freescale Semiconductor / Motorola, AN2127 Datasheet - Page 4

• Manufacturer Part Number: AN2127
• Description: EMC Guidelines for MPC Based Automotive Powertrain Systems
• Manufacturer: Freescale Semiconductor / Motorola

Freescale Semiconductor, Inc.
Vias
Trace
Capacitor
Capacitor
Solder Pads
Correct
Incorrect
Figure 1 Vias for Decoupling Capacitors
The remaining 22 10 nF capacitors are required for decoupling the low-voltage (3.3-V or 2.6-V) MCU
supply. The MPC55x and the MPC56x have different ball maps. Also, some application boards allow
for component placements on both sides of the PCB whereas some only allow for component place-
ment on one side of the PCB. Therefore, four different strategies for the layout of the remaining 22 ca-
pacitors are presented in order to accommodate all of the possibilities.
1. MPC55x Double-Sided Component Placement Application
The basic strategy in this situation is to connect all the low-voltage power supply balls (V
and N
)
DDI
VDDL
to the low-voltage power supply plane. The plane is then decoupled by connecting the capacitors direct-
ly to the power and ground planes. Start by placing as many capacitors directly opposite the MCU (on
the other side of the PCB) between the vias from the center and outer rows of balls (see
Figure
2). Place
any remaining capacitors on the opposite side of the PCB as the MCU just outside the vias from the
outer row of balls uniformly distributed around the MCU. All V
balls should be connected directly to
SS
the ground plane.
EMC Guidelines for MPC500-Based Automotive Powertrain Systems
MOTOROLA
Rev. 0, 15 July 2001
4
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