Research On The Key Technologies Of DC-DC Buck Converter Based On Adaptive On-time Control

With the rapid development of 5G communication,Internet of Things(IoT)and factory automation and control,high-efficiency and high-reliability power management chips have been widely used and are one of the most critical core devices in modern electronic equipment.In order to meet the sundry requirements in life and industry,the functions and integration of electronic devices have also increased and became higher,respectively.At the same time,for the purpose of being cost-effective and realizing longer battery life,the DCDC power management chips not only require good performance,such as low quiescent current consumption,wide input and load range,high efficiency and small size,but also requires as few external components as possible to improve the application system integration.Adaptive on-time(AOT)control is a novel switching power supply control scheme that automatically adjusts the switching frequency of the converter according to the load.AOT control can exhibit pseudo-constant frequency characteristics in continuous conduction mode(CCM)under heavy load,which is similar to traditional pulse width modulation(PWM)control.On the other hand,in the discontinuous conduction mode(DCM),which usually occurs at light load,AOT control is similar to pulse-frequency modulation control.Therefore,this control scheme can achieve high conversion efficiency over a wide load range.Furthermore,a single control architecture can avoid mode switching in the traditional multimode control scheme,so the quiescent current consumption can be effectively reduced and a smaller chip area can also be achieved.in addition,the simple compensation network can achieve fast transient response.Firstly,the basic theory of DC-DC buck converter is discussed,and we introduce the main control technology in detail,and obtains the specific reasons for adopting the AOT control scheme.Secondly,the system-level modeling of the on-time control is carried out to obtain its general loop stability conditions,which are verified by system level simulation.In addition,the key indicators and parameter selection of the converter are analyzed in detail.Based on SMIC 0.18μm 5V CMOS process,a power management chip of nanowatt-level high-efficiency DC-DC buck converter is designed and implemented in this paper.Firstly,the on-demand modulation strategy is proposed to compress the quiescent current consumption,which can dynamically switch the ON/OFF status of power-hungry subcircuits,such as on-time generator and zero current detector,according to the work requirements.Moreover,based on the analysis of the sub-threshold operating characteristics of metal-oxide-semiconductor field-effect transistor(MOSFET),this paper proposes and designs an ultra-low power control loop to achieve nW-level power consumption,which including ultra-low power all-in-one bandgap voltage and current references,ultra-low power sleep-time detector with cycle-by-cycle real-time detection and adaptive bias and adaptive gain comparator.Finally,the proposed buck converter achieves a peak efficiency of 95.8%and>90%efficiency from 10 μA to 300mA.A 240nA quiescent current,including bandgap voltage and current reference,is achieved.With a low output ripple of less than 20 mV,the input voltage range and regulated output voltage are 2.1-5.5 and 1.8V,respectively.Based on SMIC 0.18μm 40V BCD process,a DC-DC buck converter with integrated bootstrap circuit is designed and implemented in this paper.First of all,the control scheme and low power implementation strategy of the converter refer to the design of nanowatt-level high-efficiency DC-DC buck converter.Secondly,in order to solve the problem of off-chip components in traditional bootstrap circuits,this paper proposes a fully integrated bootstrap circuit scheme to reduce external components.The timing-controlled P-type Laterally Diffused Metal-Oxide-Semiconductor Field-Effect Transistor(PLDMOS)device is used to realize the unidirectional conductivity of the diode,and the on-chip integrated capacitor stacking technology is adopted to realize the bootstrap capacitor with large capacitance.Moreover,this paper presents a bandgap voltage reference with a high-order curvature compensation circuit,which utilizes the sub-threshold characteristics of MOSFETs to generate second-order and third-order curvature currents to compensate the higher-order temperature nonlinearity of base-emitter of bipolar junction transistors(BJTs).The experimental results show that the input voltage range of the proposed converter is 6-36V,the output voltage is 5V,and the maximum load current is 1.5A.Quiescent current consumption is less than 16μat full input,with a minimum of 7.75μA.The peak efficiency is 94.1%,and the efficiency at μmA is 88.9%under 6V input condition.In order to improve the reliability of the DC-DC buck converter,some novel protection technology is proposed in this paper.Firstly,a low-power cycle-by-cycle over-current detection technology based on AOT control is proposed.This technology can effectively protect the chip when over-current or short circuit occurs in the converter.And then,a selfshutdown on-chip soft-start technique is proposed to prevent output overshoot and inrush current.Moreover,the predictive dead time control technology can effectively prevent the shoot-through phenomenon and eliminate the conduction loss of the body diode.Finally,this paper proposes a power good circuit,which provides an indication signal for the subsequent circuit.This signal represents whether the output voltage is powered on normally.The protection technologies mentioned above all give the corresponding circuit implementation and experimental results.