Methods and systems provide a partitioned IP core and hierarchical power management to reduce power consumption and footprint size of an “always-on” pulse density modulation (PDM) sensor system. The IP core may be partitioned into a register transfer level (RTL) block and a firmware block. The RTL may include a first stage decimation filter, storage, and, optionally, a sound energy detector. The firmware block may include subsequent decimation filter(s) and sensor processing logic, e.g., a sound trigger algorithm. In operation, the firmware block may conserve energy by being in a power-off or power-saving mode by default. Responsive to a trigger by the sound energy detector, the firmware block may wake up, receive data from the RTL block, and process the data. The sound energy detector may output the trigger based on characteristics of the received sample such as signal strength, noise strength, and type.