| With the rapid development of integrated circuits,various portable electronic products emerge in endlessly;consumer demand for portable electronic products is increasing,power supply is an important part of electronic products,its performance is very important to the stability and reliability of electronic products.Switching power supply has the characteristics of high conversion efficiency,small volume,light weight and strong anti-interference ability,its market share in the power market is high.It is a research hotspot of the adaptive on time control mode step-down converter switching power supply has the characteristics of simple control loop and fast transient response.At the same time,with the increase of chip integration,the power consumption of the system increases,this will cause the temperature of the chip to rise,which will have an important influence on the stability and reliability of the system.Therefore,in order to maintain the stability of the system,it is necessary to set the temperature protection circuit inside the chip.The main content of this paper is to study and design the adaptive on time timer and overtemperature protection circuit.In this paper,the background and significance of the research,the current situation and development trend of Buck switching power supply and overtemperature protection circuit are introduced;then the basic work theory foundation of Buck dc-dc converter is summarized;then the main components and working principles of the system are analyzed and introduced;then,the adaptive on time timer and overtemperature protection circuit are studied and designed,including comparator circuit,on time generation circuit,temperature detection voltage generation circuit,etc.The comparator in the adaptive on time timer circuit uses the three-stage amplifier circuit to improve the gain and reduce the transmission delay;in the on time generation circuit,the current which is proportional to the input voltage is used as the bias current,so that the conduction time can be adjusted according to the change of input and output voltage.The temperature sampling circuit in the overtemperature protection circuit is based on the temperature characteristics of the triode base-emitter,which volatility is small when the input voltage changes and it has high stability.In Cadence software,based on the 0.18?mBCD process model,Hspice software is used to perform functional simulation analysis of the circuit,simulation results show that,the typical working frequency of the system is 1.5MHz and the output voltage is 1.8V;the on time can decrease with the increase of input voltage and increase with the increase of output voltage;when the input voltage varies within the range of 3V~5.5V,the maximum operating frequency error of the system is 2.7%,when the output voltage varies within the range of 1.2V~2.4V,and the maximum error of system working frequency is 2.0%;the overtemperature protection circuit under the typical applications,the threshold of over temperature is 150.5?,the threshold of restore temperature is 130.5?,when input voltage changes within the 3V~5V,the maximum variation of over temperature threshold and restore temperature threshold is 0.01?,the hysteresis temperature is stable at 20?;Finally,the on timer and overtemperature protection circuit are simulated together;simulation results display that,the system stops working in overtemperature state;when temperature drops to the output of overtemperature protection circuit is low level,system returns to normal work.The function of overtemperature protection is realized. |
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