USB INTERFACE CIRCUIT AND METHOD FOR LOW POWER OPERATION

Described examples include USB port controllers (120-1, 120-2) with a control circuit (130) configured to switch from a normal first power mode to a second power mode (LP) for reduced power consumption in response a command (I2CIdle) from a port manager circuit (104), and to switch from the second power mode to the first power mode in response to detected activity on a communications connection (106, 108), or a detected connection of a USB device to a USB port connector (102-1, 102-2). After switching back to the first power mode in response to detected communications activity, the control circuit (130) automatically switches operation of the USB port controller (120-1, 120-2) back to the second power mode unless a communications transaction addressed to the USB port controller (120-1, 120-2) is received within a non-zero certain time after switching from the second power mode to the first power mode.