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PCB design points of USB interface

2021-12-29

PCB design points of USB interface

Dongguan Changshen Electronic Technology Co., Ltd. USB PCB technology sharing

USB: universal serial bus is a serial bus standard connecting computer system and external equipment. It is also a technical specification of input and output interface. It is applied to information communication products such as personal computers and mobile devices, and extended to photographic equipment Digital TV (set-top box), game console and other related fields. The latest generation is USB 3.1, the transmission speed is 10Gbit / s, the three-stage voltage is 5V / 12V / 20V, and the maximum power supply is 100W. The new type C plug-in is no longer positive or negative. It shows several common USB interfaces. This type of USB interface is widely used in mid products.

USB interface has the following two different definitions. Select the corresponding type of USB as required.

Layout and wiring requirements of USB interface: firstly, the USB interface is placed close to the edge of PCB and extends out of the edge of PCB to facilitate plugging; Secondly, ESD and common mode inductance devices are close to USB interface, and the order is ESD common mode inductance resistance capacitance; Similarly, pay attention to the distance between ESD and USB, leave a distance of 1.5mm, and consider post welding.

Layout of USB: the differential impedance of USB should be controlled to 90 ohm and processed in package. The total length should not exceed 1800mil; Equal length winding is similar to HDMI winding. In order to suppress electromagnetic radiation, the differential line of USB takes priority in the inner layer and ensures that the line has a complete reference plane. Otherwise, the cross division of the line will cause impedance discontinuity and increase the impact of external noise on the differential line; During the routing of USB differential, the layer change vias shall be reduced as much as possible, which will cause the discontinuity of line impedance. A pair of return ground vias shall be added at the place of each hole change for signal return layer change, and GND holes shall be added at the place of differential hole change.

If the positioning posts on both sides of the USB are connected to the protective ground, ensure that the distance from GND is 2mm when dividing, punch more holes in the protected area to ensure full connection, and use magnetic beads to jumper with GND to isolate the USB protective ground