# How to connect a TVS to protect the data lines in a USB device port?

TVS is a good practice to protect USB ports. A USB (at least 2.0) connection has the power path supplied with a 5 V source (Vbus=5V0) at the host side and the data path supplied with a 3.3 V sources (3V3) at both ends of the connection.

A TVS protecting the data lines (D+, D-), is connected like the following:

Should it be connected to 5V0 (Vbus) or 3V3? Why so? Arguments? References?

(This is especially interesting in the case of FTDI and similar ICs whose transceiver logic is supplied from the internal 3.3 V LDO.)

• What's the clamping voltage of the TVS? – Matt Young Apr 19 '15 at 16:42
• @MattYoung I think the TVS clamping voltage is a second question and depends on the connection scheme being selected. – asndre Apr 19 '15 at 16:49

tl;dr, they connect the common cathode to $V_{bus}$, which is +5V.
This additionally serves as ESD protection for $V_{bus}$.