Design Of Current Detecting Circuits In Hysteretic Current-Mode Control Buck-Boost Converter

Switching power converters are an indispensable analog circuit module for battery-operated portable electronic devices. With the development of portable electronic products, low-voltage, high integration and high efficiency are the most desires features for DC-DC converters. Hysteresis control mode is the simplest control method without the need for harmonic compensation and oscillator circuits. In this paper, current detection circuits which could be used for hysteresis current control mode buck-boost DC-DC converters were designed.This paper analyzed the working principle of hysteretic mode control, introduced and compared several traditional current detection techniques which could be applied for DC-DC converter. According to characteristics of current detection circuits used for hysteretic current-mode converters, designed the peak current detection circuit, valley circuit detection circuit, zero-crossing detection circuit. The proposed current detection circuit structure is based the on-resistance of MOS. Moreover, the current reference used for detection circuits are also designed. The core structure of the three current detection circuits (peak, valley, and zero-crossing) utilized common-gate differential detection method so as to garantee the performances when the input voltage got close to the supply voltage. The reliability of the circuits could be effectively enhanced by using the differential structure to reduce effect of fluctuations of process, supply voltage, temperature (PVT) to detection circuits. Reference current source provided reference threshold for the current detection circuits. Based on the method of current summing mode, a current reference is proposed. It utilized linear temperature compensation to improve the performance of temperature. The effect of process fluctuation to the current reference could be reduced by using trimming resistance. Finally, based on the macro model of hysteresis current-mode buck-boost system, several performances of the current detection circuit are tested. The layouts of the circuits are completed by Cadence. Simulation results demonstrate that the circuit can function under circumstance of 1.5V low-voltage; a variety of peak and valley current detection circuits threshold are no more than 30mA at any case, and the range of zero-crossing detection circuit threshold is close to 50mA.0.18μm mixed-signal CMOS process which is the fashion VLSI manufacturing process is used to simulate the current detection circuits. Design and simulation tools conclude VIEWDRAW, CADENCE and HSPICE.