App note: Improving USB system reliability with transient suppressors
Adding transient suppressors to USB devices [PDF!] can help prevent damage from static discharge. This is important because USB devices are handled without protection, carried in pockets, tossed in bags, etc.
This entry was posted in app notes and tagged app note, ESD, Texas Instruments, USB.Because frequent human interaction with the USB system occurs as a result of its attractive hot-plugging ability, there is the possibility for large ESD strikes and damage to crucial system elements. The ESD protection included on the existing hardware is typically in the 2-kV to 4-kV range for the human body model (HBD) and 200-V to 300-V for the machine model (MM). The ESD voltage levels found in a normal USB operating environment can exceed these levels.
Comments
Yes transient suppressor is a good idea, and not only for USB… All externally reachable connectors should also be protected this way!
I used the cheaper PRTR5V0U2X on my USBug LPC1343 Development Board.
For an even more compact design, you can also use the EClamp2522P, with integrated 22 ohm series resistors and 1k5 pull-up.
Noise suppression/protection for EMC is also a mandatory step for professional products!
it’s probably worth-whlle mentioning that this app note (appears) to be aimed at USB 1.1. Depending on the capacitance of the TVS you put on the lines, they can slow things down enough to cause issues with higher speed USB standards.
It’s a bit limited what TI shows there. They don’t have common mode chokes in their product line so they don’t talk about them. But in noisy environments they really do help.
This application note is better because it shows several methods of protection:
http://www.we-online.de/web/en/index.php/download/media/07_passive_bauteile_-_standard/download_center_1/application_notes_berichte/The_Protection_of_USB_20_Applications.pdf
thanks that looks quite useful!
This raises another few important questions regarding USB shielding and noise suppression:
– USB device cable shield connection – grounding it or not?
– Signal/Shield GND EMC Treatments for USB2.0 Connector Interfaces
– Noise Suppression Techniques