An NMOS-LDO Regulated Switched-Capacitor DC–DC Converter With Fast-Response Adaptive-Phase Digital Control

An LDO regulated DC-DC converter with voltage ripple suppression and adaptive dropout voltage control

“…Pulse frequency modulation (PFM) mode or pulse skip modulation (PSM) mode in light load [12] can be added to further improve efficiency in future work. Different from two independent loops in conventional hybrid systems with fixed dropout architecture [2,3,4], the digital controlled DC-DC converter in this proposed architecture takes the gate of LDO's power transistor, instead of the output of DC-DC converter, as the feedback point in combining the separate loops of DC-DC converter and LDO into a whole control loop to obtain an adaptive dropout voltage. This adaptive dropout architecture lowers the output voltage of DC-DC converter, thus lowering the LDO's dropout voltage when load current is lower than maximum load.…”

“…The performance comparison of this proposed design with prior DC-DC converter + LDO hybrid systems [2,4,7,9] is listed in Table I. LDO's dropout voltage in the designs [2,4] is constant across the entire load range whereas dropout voltage in the designs [7,9] is adaptive to load current as this work using other methods.…”

“…The performance comparison of this proposed design with prior DC-DC converter + LDO hybrid systems [2,4,7,9] is listed in Table I. LDO's dropout voltage in the designs [2,4] is constant across the entire load range whereas dropout voltage in the designs [7,9] is adaptive to load current as this work using other methods. Although designs [7,9] can also adjust LDO's dropout voltage dynamically corresponding to load current and improve overall efficiency at light load, they both need a duplicated transistor and a current sensing circuit to sense the load current, which will increase the complexity of circuits, chip area and power loss.…”

“…For designs [2,7,9], the output voltage is higher than this work so that the LDO's efficiency is theoretically high. For design [4], the full load range is only 30 mA so that its dropout voltage can be as low as 50 mV to increase efficiency. Consequently, this work effectively reduces the output voltage ripple down to the level that is comparable to or even superior than the prior designs while maintaining a comparable high and load-adaptive overall efficiency.…”

“…Several hybrid systems with different architectures [2,3,4,5,6,7,8,9,10] have been investigated. In conventional hybrid systems [2,3,4], a separate LDO is connected directly in series with a separate DC-DC converter. Thus, LDO's dropout voltage is fixed to a sufficiently large value based on maximum load to ensure a proper working region of LDO's power transistor.…”