Datasheet
PowerPC 970FX RISC Microprocessor
5.3 PLL Power Supply Filtering
The PowerPC 970FX microprocessor has a separate AVDD pin that provides power to the clock generation
PLL.
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 induc-
tance. The ferrite bead shown in Figure 5-1 should supply an impedance of less than 70 Ω in the 100 - 500
MHz region.
Note: AVDD measured at the pins of the part should never be more than 50 mV lower than the AVDD voltage
range specified in Table 3-2 Recommended Operating Conditions on page 21.
Figure 5-1. PLL Power Supply Filter Circuit
AV Power Supply Filter Circuit
DD
Discrete Resistor
2Ω
Ferrite Bead
AV Pin
DD
AV post filter (see previous note about AV .)
DD
DD
C1
C2
AV
DD
1
ANALOG_GND Pin
AV
DD
Regulator
Item
Description/Value
Resistor
C1
2 Ω
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
Page 66 of 78
Version 2.5
March 26, 2007
IBM [ IBM ]
