VREG tracks the battery until the battery voltage falls below the VREG programmed threshold (2.4, 2.5, 2.6, or 2.7V. VREG=2.7V is the RESET default). At voltages below the VREG threshold, the PMU's switching regulator turns ON and holds the VREG voltage to be no less than the threshold value for VREG load current upto 15mA. The VREG voltage then, will be a saw tooth waveform that can be ~10Hz to 110KHz and with ripple of 20mVpp to 110mVpp depending on VREG load current and VBAT voltage from 1.8V to VREG programmed threshold. The rise slope of the sawtooth is nearly constant but the amplitude is a function of VBAT. The fall slope is VREG load current dependant. The minimum voltage of the sawtooth waveform should be greater than or equal to the VREG programmed threshold over the VREG load current range.