摘要
电源是现代电子设备不可缺少的一部分,为了适应现代电子设备的小型、轻量及高性能等要求,本课题基CMOS工艺,并利用HSPICE仿真工具,设计了一种高效率升压型DC/DC转换器。内容包括芯片电路的工作原理、设计以及仿真,并完成了芯片的版图设计及物理验证。
首先,在芯片中采用了同步整流技术和轻负载条件下的自动突发模式。同步整流部分采用低导通阻抗的功率PMOS管代替肖特基二极管起整流管作用,使整流管上的损耗降至肖特基二极管损耗的1/3以下,极大地提高了效率。轻负载条件下的自动突发模式操作可以在输出负载电流降至内部设定门限值以下时,立即关断芯片的大部分电路,当输出电压从标称值下降了1%左右时,DC/DC转换器会被唤醒,并开始正常的PWM操作,从而使轻负载条件下的效率大大提高。
其次,针对芯片的不连续工作模式,设计了零电流比较器和抗振铃模块。零电流比较器可以防止电感器电流达到零之后立即变至负值,减少由负电感器电流引起的损耗。抗振铃模块通过在芯片内部利用一个传输门将Vin和SW短接,产生阻尼来防止电感器电流降至零时产生高频振铃,有效地减少了功率损耗。
将该转换器用于一个输出电压为3.3 V的升压型开关电源系统中,HSPICE仿真结果表明,该转换器在轻、重负载时都具有高效率,在输入电压为1.5 V,负载为60 mA时达到最高值92.78%。
Power supply is necessary for modern electronic devices and equipment. To satisfy requirements of compact electronic instruments with high performances and small weight, a high-efficiency boost DC/DC converter is designed based on CMOS technology and using HSPICE simulation tool. The research work includes circuit operating principle, circuit system design, simulation, and layout design, physical validation.
First, synchronous rectification technology and automatic Burst Mode operation at light loads are designed in the chip. The synchronous rectification technology replaces the schottky diode with a low on-resistance power MOSFET, so the rectifier’s power losses has decreased to schottky diode’s power loss’s 1/3 and the efficiency of the converter has been increased. Burst Mode operation is initiated if the output load current falls below an internally programmed threshold. Once initiated, the burst mode operation circuitry shuts down most of the device. When the output voltage has dropped approximately 1% from nominal, the chip wakes up and commences normal PWM operation. This operation has improved efficiency of the converter at light loads.
Second, a zero current comparator and anti-ringing module are proposed for the Discontinuous-Conduction Mode (DCM) of the converter. The zero current comparator can prevent the inductor current from reversing in polarity improving efficiency at DCM. The anti-ringing module prevents high frequency ringing of the SW pin as the inductor current goes to zero by connecting the Vin pin and the SW pin with a transmission gate. This converter has successfully been used for a 3.3 V step-up switching regulator system, and high efficiency at both light and heavy loads is confirmed through HSPICE simulation, with the highest efficiency of 92.78% when the input voltage is 1.5 V and the load current is 60 mA.
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