After analyzing the principle of the entire circuit, you can begin to lay out the entire circuit. Below, I will introduce the ideas and principles of the layout.
1. First of all, we will place the components with structural requirements. When placing, according to the imported structure, the connector must pay attention to the placement of pin 1.
2. Pay attention to the height limit requirements in the structure during layout.
3. If you want a beautiful layout, you usually locate it according to the outer frame or center line coordinates of the component (center alignment).
4. The overall layout should consider heat dissipation.
5. When laying out, it is necessary to consider the wiring channel evaluation and the space required for the length of time.
6. It is necessary to consider the power flow direction and evaluate the power supply channel during layout.
7. High-speed, medium-speed, and low-speed circuits should be separated.
8. Keep strong current, high voltage and strong radiation components away from weak current, low voltage and sensitive components.
9. The analog, digital, power and protection circuits should be separated.
10. The interface protection device should be placed as close to the interface as possible.
11. Requirements for the placement sequence of interface protection devices:
Generally, the order of power supply lightning protection devices is: varistor, fuse, suppression diode, EMI filter, inductor or common mode inductor. For the lack of schematic diagram, any of the above components are extended.
Generally, the order of the protection devices for interface signals is: ESD (TVS tube), isolation transformer, common mode inductor, capacitor, and resistance. For any missing components in the schematic diagram, follow the sequence of the schematic diagram (you must have a judgment schematic diagram). Is it correct ability) to carry out "one-line" layout.
12. The level conversion chip (such as RS232) is placed close to the connector (such as serial port).
13. Devices that are susceptible to ESD interference, such as NMOS and CMOS devices, should be as far away as possible from areas that are susceptible to ESD interference (such as the edge area of a single board).
14. Clock device layout:
Crystals, crystal oscillators and clock distributors should be as close as possible to related IC devices;
The filter of the clock circuit (try to use the "∏" filter) should be close to the power input pin of the clock circuit;
Whether the output of the crystal oscillator and the clock distributor is connected in series with a 22 ohm resistor;
Whether the useless output pins of the clock distributor are grounded through resistors;
The layout of crystals, crystal oscillators and clock distributors should be kept away from high-power components, heat sinks and other heat-generating devices;
Whether the distance between the crystal oscillator and the edge of the board and the interface device is more than 1 inch.
15. Is the switching power supply far away from AD\DA converters, analog devices, sensitive devices, and clock devices.
16. The layout of the switching power supply should be compact, the input and output should be separated, and the layout should be strictly in accordance with the requirements of the schematic diagram, and the capacitors of the switching power supply should not be placed randomly.
17. Capacitors and filter components:
The capacitor must be placed close to the power pin, and the smaller the capacitance, the closer the capacitor is to the power pin;
The EMI filter should be close to the input port of the chip power supply;
In principle, each power supply pin has a small capacitor of 0.1 uf, and an integrated circuit one or more large capacitors of 10 uf, which can be increased or decreased according to specific conditions.
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