EMC protection of USB applications: Page 3 of 4

April 17, 2015 //By Jochen Baier, Würth Elektronik eiSos
EMC protection of USB applications
The USB port has revolutionized PC peripheral devices and is becoming increasingly popular, for example in acquiring measurement data or installing software updates on machines. As a bus system for data transmission, it is found wherever mobile devices have to be connected. Although the connectors used in daily life may seem robust, those who develop USB applications must still not neglect protection of their interface.

Recommended layout for USB ports

As apparent in Figure 3, two difference signal lines (D+ and D-) are routed from the plug connector to the TVS diode and continue via the current-compensated data line choke to the USB controller. The result is outstanding ESD protection, as well as good suppression of the data line pair. VBUS is routed via the TVS diode to the SMD ferrite. After the SMD ferrite, an additional capacitor and a further SMD ferrite can be inserted to achieve the highest possible attenuation of a PI filter.

Figure 3: Protection of a USB port

In case of very sensitive ICs and/or high-reliability developments, optimized ESD protection can be achieved by double-contacting the TVS diode (art. no. 824 015) pins. (Figure 4)

Figure 4: Double protection of a USB port

Developers who prefer a single-channel protection element can use the WE-VE series ESD suppressors. These always have to be connected from D+/D- to GND. The other components are connected, as shown here. Figure 5

Figure 5: Protection with single-channel elements
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