With these several SCM Control Board design principles, the boss for you praise!

SCM Control Board in the design process, if you can follow the following several principles, the boss must praise you!

(1) In the layout of components, should be related to each other components as close as possible, for example, clock generators, crystal, CPU clock input is easy to produce noise, when placed should be close to them. For those prone to noise of the device, small current circuit, high-current circuit switching circuit, should try to keep it away from the microcontroller logic control circuit and storage circuit (ROM, RAM), if possible, these circuits can be made into a circuit board, which is conducive to anti-interference, improve the reliability of the circuit work.

(2) As far as possible in key components, such as ROM, RAM and other chips next to the installation of decoupling capacitor. In fact, printed circuit board traces, pin connections and wiring can contain a large inductance effect. A large inductor may cause severe switching noise spikes on the VCC line. The only way to prevent the switching noise spikes on the VCC line is to place a 0.1uF electronic decoupling capacitor between VCC and the power source. If a surface mount element is used on the circuit board, it can be fastened directly to the component with a chip capacitor on the VCC pin. It is best to use ceramic capacitors because they have low electrostatic loss (ESL) and high-frequency impedance, and the dielectric stability of this capacitor temperature and time is good. Try not to use tantalum capacitors, because at high frequencies, it has higher impedance.

The following points need to be taken into consideration when placing the decoupling capacitor

At the power input of the printed circuit board, the electrolytic capacitance around 100uF is bridged, and if the volume permits, the capacitance is better.

In principle, each IC chip next to the need to place a 0.01uF ceramic capacitor, if the gap is too small to place the circuit board, you can place a 1~10 tantalum capacitor around every 10 chips.

For components with a weak anti-jamming capability, large current changes during shutdown, and memory components such as RAM and ROM, the decoupling capacitor should be connected between the power line (VCC) and the ground.

The lead of the capacitor should not be too long, especially the high-frequency bypass capacitor cannot be leaded.

(3) in the single-chip microcomputer control system, there are many types of ground wire, such as systematically, shielded, logically, simulated ground, whether the ground is reasonable layout, will determine the anti-jamming ability of the circuit board.

The following questions should be considered when designing ground and connecting sites

Logically and simulated ground to separate wiring, can not be combined, their respective ground wires are connected with the corresponding power ground. In the design, the analog ground should be as bold as possible, and as far as possible to increase the grounding area of the terminal. Generally speaking, the analog signal for the input and output, and the microcontroller circuit is best separated from the optocoupler.

When designing the printed circuit version of the logic circuit, the ground wire should form a closed loop and improve the anti-jamming ability of the circuit.

The ground should be as coarse as possible. If the ground is very thin, then the ground resistance will be larger, resulting in the earth potential changes with the current changes, resulting in signal level instability, resulting in the circuit's anti-jamming ability to decline. In the case of space permitting, to ensure that the main ground wire width at least 2~3mm, the element pin on the grounding line should be around 1.5mm.

Be aware of the pick-up location. When the signal frequency of the circuit board is less than 1MHz, because the electromagnetic induction between the wiring and components is very small, and the circulation of the grounding circuit has a great influence on the interference, so we should use a little ground, so that it does not form a circuit. When the circuit board signal frequency above 10MHz, because the inductance effect of the wiring is obvious, the ground impedance becomes very large, at this time the circulation of the grounding circuit is no longer the main problem. Therefore, multi-point grounding should be used to minimize ground impedance.

Power line Arrangement In addition to the size of the current as far as possible to increase the width of the line, in the wiring should also make the power line, the direction of the wire line and the direction of the data line alignment, in the end of the wiring work, the circuit board at the bottom of the floor without traces of the place covered, these methods are helpful to enhance the circuit

The width of the data line should be as wide as possible to reduce the impedance. The width of the data cable is at least 0.3mm (12mil), which is preferable if 0.46~0.5mm (18mil~20mil) is used.

As the circuit board of a hole will bring about 10pF capacitance effect, this for high-frequency circuit, will introduce too much interference, so in the wiring, should be as far as possible to reduce the number of holes. Again, too much vias can also cause the mechanical strength of the board to be reduced.

With these several SCM Control Board design principles, the boss for you praise!