The Technique Of On-chip Compensation For DC-DC Converter In PMU

As the development of semiconductor industry and to satisfy the people’s demands,portable devices such as mobile phones and PADs are involving more and morefunctions. However, the multi-functional devices also bring two shortages, the increaseof power consumption and the increase of volume. To overcome the referred shortages,the application of PMU (Power Management Unit) is becoming more popular. Ingeneral, PMU are composed of several DC-DC converters and several LDOs (LowDropout Regulator). As the most important part of PMU, the performance and the sizeof DC-DC converters directly determine whether it is applicable for the PMU. As weknow, conventional DC-DC converters are compensated with the off-chip capacitorsand resistors. Off-chip compensation not only occupies extra size of PCB but alsoincrease the number of IO pins. Additionally, extra noise is generated. Therefore,on-chip compensated DC-DC converters are necessary for PMU.To satisfy the requirement of PMU, an on-chip compensated step-down converteris presented in this paper. With the implement of capacitor multiplier technique andsuper follower technique, the converter which adopts PD compensation is achieved. Thecapacitance is3.7pF and the resistance is600K. Additionally，the noise isolationcapability is highly improved with the adoption of input differential pair in EA.Meanwhile, the application of auto-trimming technique makes up the shortage of lowDC gain, and PWM/PSM control technique improves the light load efficiency. Theconverter is simulated and taped out with the0.13μm CMOS process. The final designindex: input voltage2.6V-4.2V, output voltage0.7V-1.5V, output current1A, switchingfrequency2M, the efficiency of light load more than80%, the efficiency of heavy load90%. The taped out chip is tested, and it indicates the design results satisfy the basicrequirements.