The battery-backed RAM (BBRAM) is one of the available options for storing the device AES key. The BBRAM is a static RAM array. When the device has power on the VCCAUX_PMC supply, the BBRAM is powered by the VCCAUX_PMC supply. When the VCCAUX_PMC supply is switched off, the device automatically switches the BBRAM power domain (BPD) using the VCC_BATT pin. The key stored in BBRAM can be stored in plain text form (red) or encrypted form (black). The BBRAM can also be cleared, which is valuable as a tamper response.
The BBRAM key memory space is 288 bits. The BBRAM contains 256 bits of the AES key and 32 bits for general purpose usage. The 256-bit AES key is available for the ROM based on its selection. When the AES key in BBRAM is selected as the AES device key, the AES key management block loads the key value into the AES.