參數(shù)資料
型號: MPC745BVT350LE
廠商: FREESCALE SEMICONDUCTOR INC
元件分類: 微控制器/微處理器
英文描述: 32-BIT, 350 MHz, RISC PROCESSOR, PBGA255
封裝: 21 X 21 MM, 2.80 MM HEIGHT, 1.27 MM PITCH, LEAD FREE, PLASTIC, BGA-255
文件頁數(shù): 33/60頁
文件大?。?/td> 1559K
代理商: MPC745BVT350LE
MPC755 RISC Microprocessor Hardware Specifications, Rev. 7.0
Freescale Semiconductor
39
System Design Information
8.2
PLL Power Supply Filtering
The AVDD and L2AVDD power signals are provided on the MPC755 to provide power to the clock
generation PLL and L2 cache DLL, respectively. To ensure stability of the internal clock, the power
supplied to the AVDD input signal should be filtered of any noise in the 500 kHz to 10 MHz resonant
frequency range of the PLL. A circuit similar to the one shown in Figure 21 using surface mount capacitors
with minimum Effective Series Inductance (ESL) is recommended. Consistent with the recommendations
of Dr. Howard Johnson in High Speed Digital Design: A Handbook of Black Magic (Prentice Hall, 1993),
multiple small capacitors of equal value are recommended over a single large value capacitor.
The circuit should be placed as close as possible to the AVDD pin to minimize noise coupled from nearby
circuits. An identical but separate circuit should be placed as close as possible to the L2AVDD pin. It is
often possible to route directly from the capacitors to the AVDD pin, which is on the periphery of the 360
BGA footprint, without the inductance of vias. The L2AVDD pin may be more difficult to route, but is
proportionately less critical.
Figure 21 shows the PLL power supply filter circuit.
Figure 21. PLL Power Supply Filter Circuit
8.3
Decoupling Recommendations
Due to the MPC755 dynamic power management feature, large address and data buses, and high operating
frequencies, the MPC755 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 MPC755 system, and the MPC755 itself requires a clean, tightly regulated source of
power. Therefore, it is recommended that the system designer place at least one decoupling capacitor at
each VDD, OVDD, and L2OVDD pin of the MPC755. It is also recommended that these decoupling
capacitors receive their power from separate VDD, (L2)OVDD, and GND power planes in the PCB,
utilizing short traces to minimize inductance.
375
250
188
150
125
400
266
200
160
133
Note: The core and L2 frequencies are for reference only. Some examples may
represent core or L2 frequencies which are not useful, not supported, or not
tested for by the MPC755; see Section 4.2.3, “L2 Clock AC Specifications,” for
valid L2CLK frequencies. The L2CR[L2SL] bit should be set for L2CLK
frequencies less than 110 MHz.
Table 17. Sample Core-to-L2 Frequencies (continued)
Core Frequency (MHz)
÷1
÷1.5
÷2
÷2.5
÷3
VDD
AVDD (or L2AVDD)
10
2.2 F
GND
Low ESL Surface Mount Capacitors
相關(guān)PDF資料
PDF描述
MPC745BPX350LE 32-BIT, 350 MHz, RISC PROCESSOR, PBGA255
MPC755BPX350LE 32-BIT, 350 MHz, RISC PROCESSOR, PBGA360
MPC755CPX400LE 32-BIT, 400 MHz, RISC PROCESSOR, PBGA360
MPC745BVT300LE 32-BIT, 300 MHz, RISC PROCESSOR, PBGA255
MPC755BVT300LE 32-BIT, 300 MHz, RISC PROCESSOR, PBGA360
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