Studies On The Stability Of Integrated Current Mode DC-DC Converters Focused On PVTL Variations

Due to the predominance of high efficiency, low cost and small size, the integrated DC-DC converters are widely used. But the further improvement of its performance is seriously restricted by the variations of Process, Voltage, Temperature and Loading(PVTL). This dissertation focuses on the stability theories and methods of the converter performance and control loop at the condition of PVTL variation. The contributions of this dissertation are listed below.1. Improved current-sensing circuitBy using the improved circuit to sense the inductor current, the sense ratio only depends on the size ratio of same type devices, and is independent of the device's parameters. So the influences of the process, temperature and voltage are nearly eliminated. The stability of current-sensing is significantly improved.2. Adaptive slope compensationThe inherent relationship between slope compensation, current-sensing, supply voltage and output voltage is discovered. Then an adaptive slope compensation theory is presented to guarantee the stability of current loop. It can be applied in any integrated synchronous switching regulators.3. Reducing the slope compensation effectThe slope compensation can weaken the loading ability at high duty cycle. In order to cancel the slope compensation effect on peak current and to get a stable load capacity at different duty cycles, a novel method to limit the inductor current is introduced skillfully.4. Curvature corrected bandgap referenceTwo kinds of curvature corrected methods are presented to improve the temperature stability of the bandgap reference. One is the piecewise linear compensation method. The whole operating temperature range is divided into some sub-ranges. In each sub-range the reference can be compensated by different linear functions to get optimum results. The narrower the sub-range is, the less the compensation error is. The other is the second degree curve compensation method. Using the square relation of the MOSFET saturated current to the overdrive voltage, a second degree compensation term is produced to correct the curve of the conventional CMOS bandgap reference. So a smaller temperature coefficient is achieved.5. Simple method of loop stability verificationThe loop stability analysis can be divided into current loop and voltage loop...