I believe these are hardware thresholds. Your best way to mitigate the issue is increasing capacitance on your power lines to smooth out brown-outs. Efficient F/W design reduces current consumption, which is conjunction with power line capacitance can allow your circuit to survive short Brown-outs.
If the supply voltage drops below the brown-out reset threshold the system will be put in the reset state. This threshold is 1.7 V and can't be configured. It doesn't look like brown-out reset can be turned OFF or configured, probably for good reason.
You can configure the power-fail comparator by enabling/disabling it and setting a threshold to get a warning of impending power failure.
See the Power Management section of the User guide for more info.
