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MCF523X bảng dữ liệu(PDF) 11 Page - Freescale Semiconductor, Inc |
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MCF523X bảng dữ liệu(HTML) 11 Page - Freescale Semiconductor, Inc |
11 / 46 page Design Recommendations MCF523x Integrated Microprocessor Hardware Specification, Rev. 2 Freescale Semiconductor 11 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 must power down. VDD should not lag OVDD 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 supplies. 5.3 Decoupling • Place the decoupling caps 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 Section 7, “Preliminary Electrical Characteristics.” 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. |
Số phần tương tự - MCF523X_06 |
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Mô tả tương tự - MCF523X_06 |
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