Research On Low Dropout Regulator With Wide Power Supply Range In Smart Battery System

On-chip power converter is used to meet the requirements of different supply voltages in the power management of portable electronic devices. Because of the comprehensive advantages of low dropout, high efficiency, low noise and so on, Low Dropout Linear Regulator stands out in many kinds of regulators and grows into a popular technology.The LDO based on this thesis is applicable for Lithium-ion battery pack dedicated to smart battery system. As the Li-ion battery voltage can decrease significantly by time, the designed LDO is needed to supply a stable 1.8V output and afford load current of 20mA when the power supply ranged from 4.5 to 28 voltages.The paper first introduces the general situation, basic theory and topology of LDO regulator, and then make a deep DC analysis, AC analysis and transient analysis of the feedback loop of the regulator. After considering each module and fundamental characteristic parameters, a LDO linear regulator is designed here to convert a high voltage 4.5~28V to a stable 1.8V. By utilizing pre-regulator to output a rough 3.3V as internal power supply, the proposed LDO provides less power dissipation and high stability. In this pre-regulator module, we put the output pole of the amplifier as the dominant pole with miller compensation. But in the core LDO frequency scheme, to make sure the stability in full load range, the core regulator should utilize a 2.1uF off-chip capacitor to set the dominant pole, add a buffer stage to avoid the generation of pole in lower frequency. To level the phase margin decreased by two low frequency pole, RC compensation network in the output of differential input stage is presented to introduce an additional zero. Beyond the unit gain frequency, phase-lead compensation and ESR compensation is used to compensate poles in high frequency.The schematic and layout is designed by using TSMC 0.5um HV40V standard CMOS technology. The LDO has a wide input voltage range(4.5-28V), it can supply a stable 1.8V output and afford load current of 20mA during the temperature of -40℃~85℃.The ripple of the output voltage is less than 40mV when a current pulse draws-out from the LDO. For the DC characteristics, the line regulation is 0.00083%, the load regulation is 0.0026mV/mA, quiescent current is 126~136uA. The area of the whole layout is 1300um×2000um.