The Design Of Boost Converter With Peak Current-Mode

Portable battery-operated devices are more and more popular today. For these devices, small size, light weight and long battery run-time are the main demands. DC-DC power management chip as a voltage converter module between battery and internal working modules is very important. Its efficiency will have an impact on the battery run-time of portable devices. In order to extend the run-time of battery, it is critical to enhance the efficiency of the power management chip. In addition, the input voltage or output load may fluctuate. To control the output voltage in the required range, the power management chips should have both good load regulation and good line regulation.In this paper, a peak current mode PWM boost converter chip is designed. It could provide a stable DC voltage for the internal modules of portable electronic devices. The operating voltage of the boost converter is from 2.2V to 4V, the operating frequency is 1MHz, the output voltage is from 3V to 5V, and the output load is from 50mA to 200mA. The boost converter chip adopting N-type power MOSFET and on-chip compensation circuit is to reduce the number of PIN and the chip area.The boost converter system primarily includes two parts. One is the power stage circuit; the other is the control circuit. Power stage circuit consists of the inductor, power MOSFET, diode,output capacitor and other power stage components. The loss of the converter mainly occurred in the power stage circuit. In order to enhance the efficiency of the converter, the power stage components are designed to meet the requirements mentioned above. In designing of the power MOSFET, the width-to-length ratio is determined by the analysis which is about the conduction loss and switching loss. In designing of the Inductor, it is necessary to consider the peak-to-peak inductor current and the value of the inductor DCR. In designing of the output capacitor, the ripple of the output voltage should be considered. And the zero impact, which is caused by the output capacitor and its equivalent series resistance, on the system stability should also be considered. In order to estimate the stability of the system and set guidance for designing compensation circuit, the system transfer function is derived and analyzed. The peak current-mode boost converter system includes two loops: one is current loop; the other is the voltage loop. In this paper, the transfer function of the power stage is derived firstly. And then, the closed-loop current transfer function is derived. Finally, the open-loop voltage transfer function is derived through the closed- current loop transfer function and the power stage transfer function. The analysis results show that there are a dominant pole depending on the value of the load resistance and the Output capacitance, a right-half-plane zero depending on the load resistance and the inductance and a left-half-plane zero depending on the inductance. The zero and pole of the compensation circuit, which could make the system has fast transient response speed, good linear adjustment and good load regulation, can be determined by the analysis and the simulation results.The boost converter control circuit consists of error amplifier, comparator summation, soft-start module, module bandgap reference, current detection module, oscillator module and the slope compensation module. The design of the error amplifier is very critical. The system compensation circuitry is realized through the design of the error amplifier. The current detection circuit adopts lossless testing technology with the purpose of decrease loss and increase the system bandwidth. In order to avoid the damage introduced by the inrush current, the soft-start module is added to the converter. And the inrush current is limited.The peak current-mode boost converter designed here adopts 0.35μm CMOS process, and simulates by Cadence Spectre. The results of the simulation show that the highest efficiency is 87.4%, the load regulation is 0.16%/A (load current from 50mA to 200mA), the line regulation is 0.44%/V (and input voltage from 2.2V to 4V), the maximum output voltage ripple is 10mV, and the inrush current is less than 1.2A. The boost converter has achieved the design goal.