The TUSB1044 monitors the physical layer conditions like receiver termination, electrical idle, LFPS, and SuperSpeed signaling rate to determine the state of the USB3.1 interface. Depending on the state of the USB 3.1 interface, the TUSB1044 can be in one of four primary modes of operation when USB 3.1 is enabled (CTL0 = H or CTLSEL0 = 1b1): Disconnect, U2/U3, U1, and U0.

The Disconnect mode is the state in which TUSB1044 has not detected far-end termination on both upstream facing port (UFP) or downstream facing port (DFP). The disconnect mode is the lowest power mode of each of the four modes. The TUSB1044 remains in this mode until far-end receiver termination has been detected on both UFP and DFP. The TUSB1044 immediately exits this mode and enter U0 once far-end termination is detected.

Once in U0 mode, the TUSB1044 redrives all traffic received on UFP and DFP. U0 is the highest power mode of all USB3.1 modes. The TUSB1044 remains in U0 mode until electrical idle occurs on both UFP and DFP. Upon detecting electrical idle, the TUSB1044 immediately transitions to U1.

The U1 mode is the intermediate mode between U0 mode and U2/U3 mode. In U1 mode, the TUSB1044 UFP and DFP receiver termination remain enabled. The UFP and DFP transmitter DC common mode is maintained. The power consumption in U1 is similar to power consumption of U0.

Next to the disconnect mode, the U2 and U3 mode is next lowest power state. While in this mode, the TUSB1044 periodically performs far-end receiver detection. Anytime the far-end receiver termination is not detected on either UFP or DFP, the TUSB1044 leaves the U2 and U3 mode and transition to the Disconnect mode. It also monitors for a valid LFPS. Upon detection of a valid LFPS, the TUSB1044 immediately transitions to the U0 mode. In U2 and U3 mode, the TUSB1044 receiver terminations remains enabled, but the TX DC common mode voltage is not maintained.

When SLP_S0# is asserted low, it disables Receiver Detect functionality. While SLP_S0# is low and TUSB1044 is in U2 and U3, TUSB1044 disables LOS and LFPS detection circuitry and RX termination for both channels remains enabled. This allows even lower TUSB1044 power consumption while in the U2 and U3 mode. Once SLP_S0# is asserted high, the TUSB1044 will again start performing far-end receiver detection as well as monitor LFPS so it can know when to exit the U2 and U3 mode.

When SLP_S0# is asserted low and the TUSB1044 is in Disconnect mode, the TUSB1044 will remain in Disconnect mode and never perform far-end receiver detection. This allows even lower TUSB1044 power consumption while in the Disconnect mode. Once SLP_S0# is asserted high, the TUSB1044 will again start performing far-end receiver detection so it can know when to exit the Disconnect mode.