Noteworthy design principles of single chip microcomputer control board

rain

Noteworthy design principles of single chip microcomputer control board [Copy link]

The following principles should be followed in the design of microcontroller control boards:
　　(1) In terms of component layout, related components should be placed as close as possible. For example, clock generators, crystal oscillators, and CPU clock inputs are prone to noise, so they should be placed closer together. For those devices that are prone to noise, small current circuits, large current circuits, switching circuits, etc., they should be kept as far away from the logic control circuits and storage circuits (ROM, RAM) of the microcontroller as possible. If possible, these circuits can be made into circuit boards separately, which is conducive to anti-interference and improves the reliability of circuit operation.

　　(2) Try to install decoupling capacitors next to key components such as ROM, RAM and other chips. In fact, printed circuit board traces, pin connections, and wiring may contain large inductance effects. Large inductance may cause severe switching noise spikes on the Vcc trace. The only way to prevent switching noise spikes on the Vcc trace is to place a 0.1uF electronic decoupling capacitor between VCC and the power ground. If surface mount components are used on the circuit board, chip capacitors can be used directly close to the components and fixed on the Vcc pin. It is best to use ceramic capacitors because they have low electrostatic loss (ESL) and high-frequency impedance. In addition, the dielectric stability of this capacitor over temperature and time is also very good. Try not to use tantalum capacitors because their impedance is high at high frequencies.
Connect an electrolytic capacitor of about 100uF across the power input terminal of the printed circuit board. If the volume allows, a larger capacitance is better.

In principle, a 0.01uF ceramic capacitor needs to be placed next to each integrated circuit chip. If the gap in the circuit board is too small to place it, a 1-10 tantalum capacitor can be placed for every 10 chips.
For components with weak anti-interference ability, large current changes when turned off, and storage components such as RAM and ROM, a decoupling capacitor should be connected between the power line (Vcc) and the ground line.
The lead of the capacitor should not be too long, especially the high-frequency bypass capacitor cannot have a lead.

　　(3) In the single-chip microcomputer control system, there are many types of ground wires, including system ground, shielded ground, logic ground, analog ground, etc. Whether the ground wire is laid out reasonably will determine the anti-interference ability of the circuit board. When designing the ground wire and grounding point, the following issues should be considered:

the logic ground and analog ground should be wired separately and cannot be used together. Their respective ground wires should be connected to the corresponding power ground wire. When designing, the analog ground wire should be as thick as possible, and the grounding area of the lead-out end should be as large as possible. Generally speaking, for the analog signals of input and output, it is best to isolate them from the microcontroller circuit through an optocoupler.
When designing the printed circuit board of the logic circuit, its ground wire should form a closed loop to improve the anti-interference ability of the circuit.
The ground wire should be as thick as possible. If the ground wire is very thin, the ground wire resistance will be large, causing the ground potential to change with the change of current, resulting in unstable signal level and reduced anti-interference ability of the circuit. If the wiring space allows, the width of the main ground wire should be at least 2 to 3 mm, and the ground wire on the component pin should be about 1.5 mm.
Pay attention to the selection of the grounding point. When the signal frequency on the circuit board is lower than 1MHz, since the electromagnetic induction between the wiring and the component is very small, and the loop formed by the grounding circuit has a greater impact on the interference, it is necessary to use a single point grounding to prevent it from forming a loop. When the signal frequency on the circuit board is higher than 10MHz, the impedance of the ground line becomes very large due to the obvious inductance effect of the wiring. At this time, the loop current formed by the ground circuit is no longer the main problem. Therefore, multi-point grounding should be used to reduce the impedance of the ground line as much as possible.
In addition to increasing the width of the power line as much as possible according to the current size, the routing direction of the power line and the ground line should be consistent with the routing direction of the data line during routing. At the end of the wiring work, the ground line is used to cover the bottom layer of the circuit board where there is no routing. These methods are helpful to enhance the anti-interference ability of the circuit.
The width of the data line should be as wide as possible to reduce the impedance. The width of the data line should be at least not less than 0.3mm (12mil), and it is more ideal if 0.46~0.5mm (18mil~20mil) is used.
Since a via on the circuit board will bring about a capacitance effect of about 10pF, this will introduce too much interference for high-frequency circuits, so the number of vias should be reduced as much as possible during routing. In addition, too many vias will also reduce the mechanical strength of the circuit board.　
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mdreamj

very good

rain

Thank you, I hope we can develop together.

lorant

That's pretty good.

rain

Well, I received it.