What external circuitry do I need to connect the MAX3420E to a USB?
The MAX3420E requires a VCC supply of 3.3V. Bus-powered peripherals need a 3.3V regulator to convert the power available on the VBUS pin (4.4V to 5.25V) to 3.3V. In addition, the MAX3420E requires an external crystal (parallel resonant, 12MHz ±0.25%) with load capacitors from each pin to ground, and two series resistors (33Ω, 1%) between the D+/D- outputs, and the USB "B" connector.
