By using the function called Low Energy Mode, it is possible to reduce current consumption without compromising USB functionality.

USB does not always transmit data (TX) or receive data (RX), but has a standby (IDLE) state, but as shown in the figure below, the same amount of current is consumed during standby as during data reception. doing.

Low Energy USB has a mechanism to automatically lower the consumption current during this IDLE period, and the consumption current in the green part in the figure below can be reduced. The effect of reducing current consumption depends on the application, but in the case of Silicon Labs' sample code (HD Keyboard), we were able to confirm a 5-35% reduction in current consumption. See AN0886 (Happy Gecko Low Energy USB Overview) for more details.