Design of a wide input supply range buck-boost converter

Buck-boost converters allow the flexibility of stepping-up and stepping-down the input supply to generate a regulated output, thus making them very attractive for applications with wide input supply range. Currently, off-the-shelf buck-boost converters require a minimum operating voltage of 1.8V. As a result, the operating conditions in which these applications are functional are severely limited. Recently, boost converters which can operate with a minimum supply voltage of 0.3V are introduced and they are designed for applications utilizing solar cells as an energy source. However, boost converters are only capable of stepping-up the input supply. In this project, the concepts implemented for these boost converters are modified and extended for use in buck-boost converter implemented using the conventional inverting topology. The converter is designed for low-power applications and it caters to a maximum load of 25mA. Special startup circuitries are designed to ensure that the startup inductor current peak is controlled, without damaging the device and to allow startup operations with minimal input voltage. In addition, a novel internal power management system is implemented and it allows for continual steady-state operations even as input drops to 0.3V. The converter operates in Pulse Frequency Modulation (PFM) mode during steady-state. Synchronous rectification operations are supported for the buck-boost converter through the implementation of a novel anti-backflow current system which greatly reduces the quiescent current consumption. The converter is designed in AMS High-Voltage 0.35µm process. The dimension of the layout implementation is 2.519mm by 2.371mm. Simulation results have shown that the converter consumes only 10.77µA and is able to startup with input supply of 0.75V typically. In addition, the converter is able to remain in steady-state operations even as input drops to 0.30V. With an input of 5.0V and an external load of 25mA, the designed converter possesses a conversion efficiency of 88.3%.

Author dc:creator

• TAN KAH YONG

• DC/DC converter, Buck-boost converter, Inverting, Low-power, Wide input range