MPC8540CPX667JC datasheet(90/104 Pages) FREESCALE

90 / 104 page

MPC8540 Integrated Processor Hardware Specifications, Rev. 4

Freescale Semiconductor

System Design Information

17.3 Decoupling Recommendations

Due to large address and data buses, and high operating frequencies, the MPC8540 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 MPC8540 system, and the MPC8540

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, GVDD, and LVDD pins of the

MPC8540. These decoupling capacitors should receive their power from separate VDD, OVDD, GVDD,

LVDD, and GND power planes in the PCB, utilizing short traces to minimize inductance. Capacitors may

be placed directly under the device using a standard escape pattern. Others may surround the part.

These capacitors should have a value of 0.01 or 0.1 µF. Only ceramic SMT (surface mount technology)

capacitors should be used to minimize lead inductance, preferably 0402 or 0603 sizes.

In addition, it is recommended that there be several bulk storage capacitors distributed around the PCB,

feeding the VDD, OVDD, GVDD, and LVDD 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—100–330 µF (AVX TPS tantalum or Sanyo

OSCON).

17.4 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, GVDD, or LVDD as required. 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, GVDD, LVDD, OVDD, and GND pins of

the MPC8540.

17.5 Output Buffer DC Impedance

The MPC8540 drivers are characterized over process, voltage, and temperature. There are two driver

types: a push-pull single-ended driver (open drain for I2C) for all buses except RapidIO, and a

current-steering differential driver for the RapidIO port.

To measure Z0 for the single-ended drivers, 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 52). The

output impedance is the average of two components, the resistances of the pull-up and 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.

MPC8540CPX667JC 数据表(PDF) 90 Page - Freescale Semiconductor, Inc

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