參數(shù)資料
型號: MC7457VG867NC
廠商: FREESCALE SEMICONDUCTOR INC
元件分類: 微控制器/微處理器
英文描述: 32-BIT, 867 MHz, RISC PROCESSOR, CBGA483
封裝: 29 X 29 MM, 3.22 MM HEIGHT, 1.27 MM PITCH, ROHS COMPLIANT, CERAMIC, BGA-483
文件頁數(shù): 50/73頁
文件大小: 1715K
代理商: MC7457VG867NC
MPC7457 RISC Microprocessor Hardware Specifications, Rev. 7
54
Freescale Semiconductor
System Design Information
response time necessary. They should also be connected to the power and ground planes through two vias
to minimize inductance. Suggested bulk capacitors: 100–330 F (AVX TPS tantalum or Sanyo OSCON).
9.4
Connection Recommendations
To ensure reliable operation, it is highly recommended to connect unused inputs to an appropriate signal
level. Unused active low inputs should be tied to OVDD. Unused active high inputs should be connected
to GND. All NC (no-connect) signals must remain unconnected.
Power and ground connections must be made to all external VDD, OVDD, GVDD, and GND pins in the
MPC7457. If the L3 interface is not used, GVDD should be connected to the OVDD power plane, and
L3VSEL should be connected to BVSEL; the remainder of the L3 interface may be left unterminated.
9.5
Output Buffer DC Impedance
The MPC7457 processor bus and L3 I/O drivers are characterized over process, voltage, and temperature.
To measure Z0, an external resistor is connected from the chip pad to OVDD or GND. Then, the value of
each resistor is varied until the pad voltage is OVDD/2 (see Figure 25).
The output impedance is the average of two components, the resistances of the pull-up and pull-down
devices. When data is held low, SW2 is closed (SW1 is open), and RN is trimmed until the voltage at the
pad equals OVDD/2. RN then becomes the resistance of the pull-down devices. When data is held high,
SW1 is closed (SW2 is open), and RP is trimmed until the voltage at the pad equals OVDD/2. RP then
becomes the resistance of the pull-up devices. RP and RN are designed to be close to each other in value.
Then, Z0 = (RP + RN)/2.
Figure 25. Driver Impedance Measurement
Table 21 summarizes the signal impedance results. The impedance increases with junction temperature
and is relatively unaffected by bus voltage.
OVDD
OGND
RP
RN
Pad
Data
SW1
SW2
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