The Brown-out-Detector(BOD) monitors VDDCORE. It is active by default. It can be deactivated by software through the Supply Controller (SUPC_MR). It is especially recommended to disable it during low-power modes, such as wait or sleep modes.
If VDDCORE goes below the threshold voltage, the reset of the core is asserted. For more information, refer to Supply Controller (SUPC) and Electrical Characteristics for SAM V70/V71.