XR22417 Datasheet, PDF (8/17 Pages) Exar Corporation – USB 2.0 7-Port Hub

XR22417
Applications Information
Functional Description
The XR22417 hub has a multiple transaction translator architecture that provides one Transaction Translator (TT)
for each of the downstream USB ports. The transaction translators allow the USB 2.0 hub to take incoming high speed
packets from the USB host on the upstream port and translate these commands, if necessary to full or low speed devices
on any of the 7 downstream ports. The MTT architecture allows for higher bandwidth as the 7 individual ports are not
constrained by a shared resource.
USB Interface
The hub function of the XR22417 supports one configuration and supports all USB endpoints:
■■ Control endpoint
■■ Interrupt-in and interrupt-out endpoints
■■ Bulk-in and bulk-out endpoints
■■ Isochronous-in and isochronous-out endpoints
The XR22417 may be placed into a low power or suspended state by the USB host. The XR22417 hub may only be utilized
in self-powered mode. Each of the downstream ports may draw up to 500mA.
Operating the XR22417 in bus powered mode violates the USB specification, as the device reports as self-powered in
USB descriptors. A bus powered hub must provide 100mA on each downstream port but a 7-port hub cannot since it can
only draw 500mA maximum from the USB host.
USB Vendor ID
Exar’s USB vendor ID is 0x04E2.
USB Product ID
Exar’s USB hub product ID is 0x0417.
Device Reset
The XR22417 has both an automatic power-up reset and an external hardware pin reset. Strapping options selected by
tying pins to logic ‘0’ or logic ‘1’ states are sampled at either reset and the resulting hardware configuration selected by the
strapping is then set. Refer to Tables 2 and Table 3.
REV1A
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