Data Sheet
Preliminary
PowerPC® 750CXr RISC Microprocessor
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 30Ω in the 100MHz region (Murata
BLM21P300S or similar).
Figure 6-1. PLL Power Supply Filter Circuit
2
Ω
FB
VDD
AVDD
0.1µF
GND
10µF
6.3 Decoupling Recommendations
Due to the PowerPC 750CXr’s feature large address and data buses, and high operating frequencies, the
PowerPC 750CXr 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 750CXr system, and the PowerPC 750CXr 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 750CXr. 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 10µF 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), 0.01µF (ceramic X7R), and 0.1µf (ceramic X7R). Suggested values for the
OVDD pins: 0.01µF (ceramic X7R), 0.1µf (ceramic X7R), and 10µF (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: 100µF (AVX TPS tantalum) or 330µF (AVX TPS tantalum).
750cxr_DD4.0_Dev_gen_4_mkt.fm
February 28, 2005
System Design Information
Page 35 of 43
IBM [ IBM ]
