A dual mode regulator, having a high current PWM regulator mode and a low
current LDO regulator mode, briefly changes the operating parameters of
the PWM and LDO regulators during a transition between modes. Changes
during the transition period include: raising the error amplifier
reference voltage of the LDO or PWM regulator to ensure a definite
handover, raising the bias current in the LDO stages during the
transition to cause the LDO regulator to quickly and stably respond to
voltage glitches, and augmenting the LDO regulator series pass
transistors with one or more additional pass transistors during the
transition to enable the LDO regulator to handle higher currents. After
the transition, the operating parameters of the enabled regulator portion
are reset to their nominal values. The PWM regulator is started with a
soft start routine to limit current through the power transistor. If the
PWM regulator uses a synchronous rectifier, a reverse current limiting
circuit is preferably used to limit reverse current when the PWM
regulator is starting up to avoid loading down the LDO regulator.