ESD Protection For USB

There are a number of solutions for connecting your do-it-yourself project to a computer. Serial ports are easy to use, even if you have to do so via a universal serial bus (USB). The advantage of going through a USB port is that operating systems already include the drivers for defined types of data.

For example, USB uses classes that allow the operating system (OS) to load the appropriate driver. In this way, the application can access the port in a standard way, which simplifies programming, since everything is welldocumented and rich examples are readily available on the web. However, when it comes to your USB project, it is a good practice to include an electrostatic discharge (ESD) protection circuitry in your project to protect the USB lines. Since the USB project will be often plugged/unplugged, it is definitely a good idea to safeguard USB lines using dedicated chips such as USBLC6-2SC6 from ST (www.st.com).

ESD Protection With Very Low Capacitance

The USBLC6-2SC6 is a monolithic application specific device dedicated to ESD protection of high speed interfaces, such as USB 2.0, Ethernet links, SIM card interfaces, and video lines. The very low line capacitance offered by the USBLC6-2SC6 (available in SOT23-6L package) secures a high level of signal integrity without compromising in protecting sensitive chips against the most stringently characterized ESD strikes.

(USBLC6-2SC6: Package and Functional Diagram)

Note that the marking on the SOT23-6L package of USBLC6-2SC6 is “UL26”. The figure shown below reveals the footprint dimension of USBLC6-2SC6 (SOT23-6L) in millimeters.

(SOT23-6L package: Footprint Dimension)

Application Hints

While the USBLC6-2SC6 provides high immunity to ESD surge, efficient protection depends on the layout of the circuit board. In the same way, with the rail to rail topology, the track from data lines to I/O pins, from VCC to VBUS pin and from GND plane to GND pin must be as short as possible to avoid overvoltages due to parasitic phenomena. A good precaution to take is to put the protection device as close as possible to the disturbance source, generally the connector. Recommended circuit board (PCB) layout of USBLC6-2SC6 is shown below. Value of the CBUS capacitor is 100nF (0.1 uF).

(Recommended circuit board layout)

 

(USBLC6-2SC6 in a home-made prototype)

If you want to add ESD protection for your existing/upcoming sensitive USB electronics project, then route the USB lines through the USBLC6-2SC6 chip as indicated in this wiring diagram.

  

Source By: circuitsdiagramlab