Data Sheet
PowerPC 970FX
Preliminary
5.3 PLL Power Supply Filtering
The PowerPC 970FX microprocessor has a separate AVDD pin which provides power to the clock generation
phase-locked loop.
To ensure stability of the internal clock, filter the power supplied to the AVDD PLL using a circuit similar to
figure 5-1. To ensure that the capacitor filters out as much noise as possible, the capacitor should be placed
as close as possible to the AVDD and ANALOG_GND pins. The capacitor used should have minimal
inductance. The ferrite bead (FB) shown in Figure 5-1 should supply an impedance of less than 70Ω in
the100-500 MHz region.
Figure 5-1. PLL Power Supply Filter Circuit
AV Power Supply Filter Circuit
DD
Ferrite Bead
2Ω
AV Pin
DD
AV
DD
C1
C2
1
ANALOG_GND Pin
AV
DD
Regulator
Item
Description/Value
2Ω
Resistor
C1
0.1 µF X7R
10.0 µF Y5V
C2
Ferrite Bead
Murata BLM21P300SN1 or similar
Notes:
1. Connected to analog ground without a filter.
System Design Information
October 14, 2005
Page 60 of 74
IBM [ IBM ]
