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PACUSBU
Upstream USB Port Terminator
Product Description The PACUSB−U1, PACUSB−U2, and PACUSB−U3 are
single−channel USB upstream−port termination networks. The PACUSB−U1/U2/U3 integrate EMI/RFI filter components R1
and C1, as recommended by the USB specification. Because these are upstream USB devices, they are terminated with a single 1.5 kW pull−up resistor to V3.3 (R2).
There are three options for the value of the series resistor R1:
For PACUSB−U1, R1 = 15 W For PACUSB−U2, R1 = 33 W For PACUSB−U3, R1 = 22 W
This series resistance plus the USB driver output resistance must be close to the USB cable’s characteristic impedance of 45 W (90 W balanced) to minimize transmission line reflections.