The ISOUSB211-Q1 device supports the additional L1 or Sleep low power state defined in the USB 2.0 Link Power Management ECN. When L1 entry is detected from the LS and FS idle state, the ISOUSB211-Q1 continues in the LS or FS idle state, at the same time reducing internal power consumption. If L1 entry is detected from HS idle state, the ISOSUB211 disables all high-speed circuits to reduce power consumption. The transition to the L1 low-power mode is completed within 50 µs.

Exit from L1 occurs through either Resume signaling from the host, on the upstream facing side of ISOUSB211-Q1, or Remote Wake signaling from the peripheral on the downstream facing side of ISOUSB211-Q1 followed by Resume signaling from the host/hub on the upstream facing side. Start of Resume or Wake are signaled by a ‘K’ state by the host or the device respectively. The end of resume is signalled by the host by driving two low-speed bit times of SE0 followed by a 'J' state. If the port was operating in high speed before entering the low power state, end of resume is signaled by the host by transitioning to the high speed idle state. ISOUSB211-Q1 is able to replicate the K signaling appropriately both upstream and downstream. After Resume/Wake signaling the device returns to LS, FS or HS idle state depending on the state it was in before entering the L1 state.