USB ports have revolutionized the development of PC peripherals and are becoming more popular, such as in applications such as acquiring measurement data or installing software updates on a machine. As a bus system for data transmission, as long as there is a place where the mobile device is connected, it has its appearance. While the connectors used in everyday life look very solid, USB application developers must still pay attention to the protection of these interfaces.
In Intel's "High-Speed ​​USB Platform Design Guide", the importance of considering the susceptibility of USB ports has even increased. Intel recommends using a current-compensated choke to suppress EMI and then use other components to prevent electrostatic discharge (ESD). Electronic devices often suffer from electrostatic discharge. Electrostatic discharge pulse voltages can be as high as 30kV and are therefore very dangerous for all types of integrated circuits. Some ICs are currently "safe" for electrostatic discharge, but this safety is only guaranteed for a small number of potential threats. Daily operations show that extra protection is essential. Only external protection measures can be taken to develop a complete circuit board that is immune to electrostatic discharge and highly reliable products. Special suppression measures are also required. Wireless networking of electronic devices is now everywhere, and their number is increasing.
It is important to protect your products from radiation interference. Only by considering the expected form of interference can the necessary suppression components be integrated in the design in time to shorten the development cycle. We know that the radiated interference of our products must also be below a certain level. This can be done with a very accurate assessment by the EMC test lab. If the product does not pass this test, the cost of rework will be several times higher than the cost of the component.
Actual anti-jamming capability
Differential mode data transmission is a significant advantage over simple coaxial cables when it comes to the effects of interference on USB. In the case of inductive interference effects (magnetic fields), the stranding of the wires can compensate for the interference effects. In view of the symmetry of the partial inductance of each twisted pair, the interference will affect the compensation effect. This anti-interference effect will be greatly reduced in practical applications.
â— The input/output of the USB controller is not completely symmetrical, so the USB signal shows common mode interference.
â— Layout is not compatible with HF/EMC, and parasitic capacitance and lack of wave resistance matching will cause common mode interference.
â— The circuit design (USB filter) is insufficient, the filter affects the signal quality, and/or the insertion loss is too low.
â— The interface design (socket, housing) is not sufficient. Poor grounding reduces the cable's shielding loss. The filter has a poor ground reference.
â— The USB cable is asymmetrical, poorly shielded, and not well grounded. Such cables can degrade signal quality, radiate signal harmonics, and provide insufficient shielding attenuation for external sources of interference.
Problem: Some of these points may not be affected, including technical implementations of outsourced USB controllers, or end users using "cheap" USB cables. Therefore, some preventive measures must be taken to prevent the interface from being affected by external interference that may damage the USB controller, while limiting the amount of interference radiation from the signal through the cable.
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