DESCRIPTION
Each device will provide termination, filtering, and ESD protection for one upstream USB port. The STF202 is an easily implemented solution for meeting the requirements of revision 1.1 of the Universal Serial Bus specification. USB line termination is achieved with series 22Ω or 30Ω resistors on both the D+ and D- USB lines. These resistors preserve signal integrity by matching the cable impedance to that of the differential driver. The 1.5kΩ pull-up resistor completes the termination circuit on each line. This resistor is required by the USB specification to identify the equipment as either a fullspeed (connected to D+ line) or low-speed (connected to D- line) device. The 47pF capacitors are used to bypass high frequency energy to ground and for edge rate control of the USB signals. Finally, the STF202 contains TVS diodes for ESD protection of both (D+ & D-) data lines and the voltage bus (VBUS). The TVS diodes provide effective suppression of ESD voltages in excess of 15kV (air discharge) and 8kV (contact discharge) per IEC 1000-4-2, level 4.
Semtech Corporation
