Data Sheet
Preliminary
PowerPC 750CXe RISC Microprocessor
750cxe_DD3.1_Dev_3_gen_mkt.fm.1.5
April 8, 2004
System Design Information
6.2 PLL Power Supply Filtering
The AVDD power signal is provided on the PowerPC 750CXe to provide power to the clock generation phase-
locked loop. To ensure stability of the internal clock, the power supplied to the AVDD input signal should be
filtered using a circuit similar to the one shown in
Figure 6-1. The circuit should be placed as close as
possible to the AVDD pin to ensure it filters out as much noise as possible. The referenced ferrite bead, FB,
shown in
Figure 6-1 should supply an impedance of approximately 30
in the 100MHz region (Murata
BLM21P300S or similar).
6.3 Decoupling Recommendations
Due to the PowerPC 750CXe’s feature large address and data buses, and high operating frequencies, the
PowerPC 750CXe can generate transient power surges and high frequency noise in its power supply,
especially while driving large capacitive loads. This noise must be prevented from reaching other components
in the PowerPC 750CXe system, and the PowerPC 750CXe itself requires a clean, tightly regulated source of
power.
Therefore, it is strongly recommended that the system designer place at least one decoupling capacitor with
a low ESR (effective series resistance) rating at each VDD and OVDD pin of the PowerPC 750CXe. It is also
recommended that these decoupling capacitors receive their power from separate VDD, OVDD, and GND
power planes in the PCB, utilizing short traces to minimize inductance.
These capacitors should range in value from 220pF to 10
F to provide both high and low-frequency filtering,
and should be placed as close as possible to their associated VDD or OVDD pins. Suggested values for the
VDD pins: 220pF (ceramic X7R), 0.01
F (ceramic X7R), and 0.1f (ceramic X7R). Suggested values for the
OVDD pins: 0.01
F (ceramic X7R), 0.1f (ceramic X7R), and 10F (tantalum). Only SMT (surface-mount
technology) capacitors should be used to minimize lead inductance.
In addition, it is recommended that there be several bulk storage capacitors distributed around the PCB,
feeding the VDD and OVDD planes, to enable quick recharging of the smaller chip capacitors. These bulk
capacitors should have a low ESR (equivalent series resistance) rating to ensure the quick response time
necessary. They should also be connected to the power and ground planes through two vias to minimize
inductance.
Suggested bulk capacitors: 100
F (AVX TPS tantalum) or 330F (AVX TPS tantalum).
Figure 6-1. PLL Power Supply Filter Circuit
V
DD
AV
DD
2
10
F
0.1
F
GND
FB