Study On Stability Of Integrated Power Management Circuit

With the development of electronic system, requirement for high efficient, reliable and convenient power management integrate circuit (PMIC) is becoming more and more urgent. Accordingly, research about this field is one of the hot issues recently. Many researches focus on the basic technology in PMIC, where stability is the key point which attracts more attention of researches.In this dissertation, the study on stability of PMIC is carried on thoroughly. Firstly, the main factors in PMIC including stability of supply, temperature and load are analyzed, which achieves an interest fact that the stability of PMIC is mainly decided by the performance of operation amplifier (OPA) it adopts. Secondly, many attentions are paid on the design of OPA and its stability, in which the zero-pole analytical method is applied to deal with the stability of OPA, and the stability is estimated by phase margin and gain. Thirdly, a high performance and high stability OPA which is suitable for PMIC is designed and utilized to a Lithium ion charger IC with thermal adjustment. The designed chip has three charger loops, including constant current, constant voltage and temperature adjustment feedback circuits. Using the research results above, the chip obtains not only high stability but also many other fine performance. The Simulation results show its final charger voltage is 4.191V, and the error is only 0.3% compared with the ideal value of 4.2V. Moreover, it owns temperature adjustment ability and adjust automatically when the temperature exceeds 120℃. Finally, the chip is fabricated with CSMC0.5um CMOS mixed-signal process. The measurement results are given as below (with reference trimming):final charger voltage is 4.19V; charger current is 510mA on the condition that the external programmable resistor is 2K.