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What are the ways to rectify the “Unknown USB Device (Device Descriptor Request Failed)” error occurring with HX2VL?
The primary reason for this error is incorrect hardware layout of HX2VL. Consider the following points:
The USB data lines should not contain any resistors or capacitors.
The RESET pin should have the minimum RC time constant value specified in the datasheet. The RESET# pin of HX2VL is generally tied to VBUS through a 10 kΩ resistor and pulled to ground through a 1 µF capacitor with a 47 kΩ resistor in parallel.
The traces on the USB data lines should be as per the USB specification.
The crystal used for HX2VL must be as per the criteria specified in the datasheet. Also, the crystal must be placed such that there is no interference with the USB data lines.
AN72332 provides the complete schematic and layout guidelines for designing a USB hub based on HX2VL.