USB 1.1 port

Circuit Protection of USB 1.1

Design Notes:

Protection Application:
The data signals used in a USB 1.1 port vary between -0.5V to +0.5V, with a maximum data rate of 12Mbps. At this data rate, the capacitance of the suppressor needs to be taken into account. The signal lines to be protected from ESD include D+ and D-. The 5VDC power bus should be protected against ESD and overcurrent events.
Solution Description:
As shown at the left, a multilayer varistor is used on the power bus for ESD protect, and a PTC is used for resettable overcurrent protection. For the data lines, discrete multilayer varistors can be used for board layout flexibility, or to reduce part count, a single Diode array can be used.
Companion Solutions:
Other solutions within the Littelfuse portfolio exist in addition to these recommendations. For example, if the operating current on the power bus is higher or lower, an appropriately rated PTC can be chosen.
Regulatory Issues:
The IEC 61000-4-2 will be the most appropriate standard that applies for this port. It supplies a test method for verifying that the end product is not susceptible to ESD events.
Unique Features:
Does not apply.
Application Warnings:
Does not apply.