A Wide Input Range Buck-Boost Converter With Smooth Transition

In recent years,with the continuous expansion of the application of the Internet of Things system,portable/implantable electronic devices have provided great convenience to human life.In order to prolong the service life of these electronic devices and reduce maintenance costs,obtaining energy from the environment for their power supply has become a promising research direction.However,the environmental energy varies widely,so the output voltage range of the transducer sensor is also very wide.Therefore,a Buck-Boost converter with a wide input range and low output ripple is needed in the self-powered system to provide a stable power supply voltage for the subsequent circuit.In order to cover the wide output voltage range of the transducer sensor and achieve low ripple output of the converter,this paper designs a wide-input Buck-Boost converter with smooth transition.In order to reduce the output voltage ripple,this paper proposes a four-mode smooth transition technology.The input voltage is divided into four intervals and four different working modes of Boost,E-Boost,Buck and E-Buck are correspondingly designed.Among them,E-Boost and E-Buck two modes can avoid extreme duty cycle(0 or 100%)when the input voltage is close to the output voltage,and achieve a smooth transition in the full input range.In order to further broaden the input range,a new type of internally integrated low-voltage startup scheme is proposed.With the help of modules such as a clock voltage doubler circuit and auxiliary power tubes,this solution uses the body diode freewheeling characteristics to realize the startup when the input voltage is lower than the threshold voltage of the power tube.In addition,in order to achieve fixed slope compensation and avoid the influence of switching noise on the duty cycle,a combined control method of peak current mode and valley current mode is proposed.Valley current mode modulation is used in Boost and E-Boost modes,peak current mode modulation is used in E-Buck and E-Buck modes,and the multiplexing of slope compensation circuits in the two modulation modes is realized.The design of the entire Buck-Boost DC-DC converter circuit and layout is based on the SMIC 0.18?m standard CMOS process,and the Cadence Spectre simulation tool is used for system-level and module circuit simulation verification.The simulation results show that the wide input Buck-Boost converter designed in this paper has an input voltage range of 0.4V?3.3V,an output voltage of 1.8V,a maximum load current of 100m A,and a switching frequency of 1MHz.The simulation results show that under light load conditions(load current 20m A),the output voltage ripple is less than 5m V,and under heavy load conditions(load current 100m A),the output voltage ripple is less than 10m V.In the best case,the output voltage ripple in the E-Buck transition mode is only increased by 5.4%compared to the Buck mode with the same load(input voltage 3.3V,load 100m A).The circuit is not disturbed when the mode is switched,and a smooth transition is achieved.The peak efficiency of the converter can reach 90.8%.The total layout area is 1.7×2.0 mm~2,of which the core circuit area is 1.4×1.5 mm~2.