A low voltage, dynamic, noninverting, synchronous buck-boost converter for portable applications

With the increasing use of low voltage portable devices and growing requirements of functionalities embedded into such devices, efficient power management techniques are needed for longer battery life. Given the highly variable nature of batteries (e.g., 2.7-4.2 V for Li-ion), systems often require supply voltages to be both higher and lower than the battery voltage (e.g., power amplifier for CDMA applications), while supplying significant current, which is most efficiently generated by a noninverting buck-boost switching converter. In this paper, the design and experimental results of a new dynamic, noninverting, synchronous buck-boost converter for low voltage, portable applications is reported. The converter's output voltage is dynamically adjustable (on-the-fly) from 0.4 to 4.0 V, while capable of supplying a maximum load current of 0.65 A from an input supply of 2.4-3.4 V. The worst-case response time of the converter for a 0.4 to 4 V step change in its output voltage (corresponding to a 0.2 to 2 V step at its reference input) is less than 300 musec and to a load-current step of 0 to 0.5 A is within 200 musec, yielding only a transient error of 40 mV in the output voltage. This paper also presents a nonmathematical, intuitive analysis of the time-averaged, small-signal model of a noninverting buck-boost converter.