描述：General Description The SMSC USB251x hub is a family of low-power, OEM configurable, MTT (multi transaction translator) hub controller IC products for embedded USB solutions. The “x” in the part number indicates the number of downstream ports available. The SMSC hub supports low-speed, full-speed, and hi-speed (if operating as a hi speed hub) downstream devices on all of the enabled downstream ports. Features Full power management with individual or ganged power control of each downstream port Fully integrated USB termination and pull-up/pull down resistors Supports a single external 3.3 V supply source; ? internal regulators provide 1.2 V or 1.8 V internal core voltage On-chip driver for 24 MHz crystal resonator or external 24/48 MHz clock input Customizable vendor ID, product ID, and device ID ESD protection up to 4 kilovolts on all USB pins Supports self- or bus-powered operation USB251xB2 and USB251xBi products support the USB Battery Charging specification Lead-free RoHS compliant packages: — 36-pin QFN (6x6 mm) — 48-pin QFN (7x7 mm) — 64-pin QFN (9x9 mm) USB251xi, USB2512Ai, and USB251xBi products support the industrial temperature range of -40oC to +85oC