Wed Nov 16 11:21:04 CST 2022
The USB interface has five endpoints: USB power (VBUS), D-, D+, signal ground (GND), and protection ground (SHIELD). In addition to the D+, D- differential signal design, the design of the USB bus power, signal ground and protection ground are equally important for the proper operation of the USB system.
USB power supply voltage of 5V, providing a maximum current of 500mA, the power lines should be arranged on the signal layer near the power supply layer, rather than on the same layer as the USB differential traces are located. The traces width should be more than 30mil to reduce its interference with the differential signal lines.
Many manufacturers of USB from the control chip operating voltage of 3.3V, when it works in bus-powered mode, requires a 3.3-5V power conversion chip, the output of the power conversion chip should be as close as possible to the voltage input of the USB chip, and the input and output of the power conversion chip should be increased capacitance capacitance and connected to a small capacity capacitor for filtering. When the USB from the control chip works in self-powered mode, the USB power line can be connected in series with a large resistor to ground.
USB interface signal GND should be in good contact with the signal GND on the PCB board, the protection ground can be placed on any layer of the PCB board, it and the signal GND split, between the two ground can be a large resistor in parallel with a high voltage capacitance, as shown in the figure below.
The spacing between the protection GND and the signal GND should not be less than 25mil to reduce the edge coupling effect between the two GNDs. Protection GND should not be covered by large area copper cladding, a 100mli width of copper foil has been able to meet the functional needs of the protective ground.
When drawing USB power lines, signal GND and protection GND, the following guidelines should be noted.
By HornmicLink_Henry @221116 11:29