MCF5275LCVM133 Просмотр технического описания (PDF) - Freescale Semiconductor

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MCF5275LCVM133

Integrated Microprocessor Family Hardware Specification

Freescale Semiconductor 

Design Recommendations

2. VDD/PLLVDD and OVDD/SDVDD should track up to 0.9 V, then separate for the completion of

ramps with OVDD/SD VDD going to the higher external voltages. One way to accomplish this is to

use a low drop-out voltage regulator.

5.2.1.2 Power Down Sequence

If VDD/PLLVDD are powered down first, then sense circuits in the I/O pads will cause all output drivers to

be in a high impedance state. There is no limit on how long after VDD and PLLVDD power down before

OVDD or SDVDD must power down. VDD should not lag OVDD, SDVDD, or PLLVDD going low by more

than 0.4 V during power down or there will be undesired high current in the ESD protection diodes. There

are no requirements for the fall times of the power supplies.

The recommended power down sequence is as follows:

1. Drop VDD/PLLVDD to 0 V.

2. Drop OVDD/SDVDD supplies.

5.3 Decoupling

• Place the decoupling capacitors as close to the pins as possible, but they can be outside the footprint

of the package.

• 0.1 µF and 0.01 µF at each supply input

5.4 Buffering

• Use bus buffers on all data/address lines for all off-board accesses and for all on-board accesses

when excessive loading is expected. See electricals.

5.5 Pull-up Recommendations

• Use external pull-up resistors on unused inputs. See pin table.

5.6 Clocking Recommendations

• Use a multi-layer board with a separate ground plane.

• Place the crystal and all other associated components as close to the EXTAL and XTAL (oscillator

pins) as possible.

• Do not run a high frequency trace around crystal circuit.

• Ensure that the ground for the bypass capacitors is connected to a solid ground trace.

• Tie the ground trace to the ground pin nearest EXTAL and XTAL. This prevents large loop currents

in the vicinity of the crystal.

• Tie the ground pin to the most solid ground in the system.

• Do not connect the trace that connects the oscillator and the ground plane to any other circuit

element. This tends to make the oscillator unstable.

• Tie XTAL to ground when an external oscillator is clocking the device.

MCF5275 Integrated Microprocessor Family Hardware Specification, Rev. 2

Freescale Semiconductor

Preliminary—Subject to Change Without Notice

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