Research And Design Implementation Of Inverting Buck-boost Converter

In recent years,Active Matrix Organic Light-Emitting Diode(AMOLED)displays have been widely used in various applications due to their high energy efficiency and superior display quality.In order to drive an AMOLED display,a bipolar power supply rail is usually required.A fixed positive voltage provides a current source for pixel-level color control,and a programmable negative voltage provides display output power for brightness control.This article focuses on the flyback Buck-boost converter that can provide negative voltage as the research object,aiming to provide high-quality negative driving power for AMOLED.In order to improve the conversion efficiency of the Buck-boost chip,this article adopts the NMOS main switching tube technology to reduce the conduction loss of the switching tube.Aiming at the problem of the gate drive capability of the NMOS main switching tube,this article uses the existing switching timing signal and the voltage switching relationship design realizes the corresponding bootstrap drive circuit.Aiming at the problem that the same type of MOS sampling resistor cannot be used due to the low gate-source voltage during the sampling process of the NMOS main switch tube,this article uses a combination of multiple resistors to achieve zero the sampling ratio of the temperature coefficient;because Buck-boost is a closed-loop highly nonlinear control system that requires a complex stability verification process,this paper studies a simpler and more suitable for engineering frequency stability verification method,using the current modulator and the corresponding relationship between the voltage loops,the loop is decomposed into two independent verification loops,and the stability verification is performed separately;in order to realize the multi-function output of Buck-boost,the 6-bit DAC programming is used to realize the programming control of the output voltage.By counting the number of pulses of the control signal,the number of pulses corresponds to the 6-bit DAC programming code,and the programming code is used to control the reference voltage at the input of the error amplifier,thereby controlling the output voltage and realizing the programmable control of the output voltage.The research results of this paper are based on the CSMC 0.18μm high-voltage BCD process to complete the specific circuit and system design,back-end and layout implementation.After comprehensive verification,when the input voltage is 2.9V to 4.5V,the switching frequency is 1.45MHz,the output voltage can be programmable from-5.4V to-1.4V,the output voltage ripple is less than 6mV at full load,and the load regulation rate is undershoot It is 16.7mV/A when overshooting,10mV/A when overshooting,7.5mV/V when undershooting,and 1.25mV/V when overshooting,and the highest conversion efficiency is 91%.