Research And Design Of A High-voltage Programmable Constant On-time Control Buck Converter

In recent years, with the increasing demand of portable products, used to providesystem power of portable products with small size and high performance voltageregulator becomes more and more important. Based on the current-mode andvoltage-mode control of power converters, the system’s transient response speed islimited because of the error amplifier and complex compensation network. Therefore,constant on-time (COT) control converters have drawn a major concern for severalimportant advantages, such as simple system structure, good transient response.Constant on-time control refers to the DC-DC converters that use the output ripplevoltage as pulse width modulation (PWM) information. Basically, requires the use oflarge equivalent series resistance (ESR) of the output capacitance can be effectivelycontrolled system. As a low-cost advantage, ceramic capacitors are widely used inconsumer power management chip, but its equivalent series resistance is very small. Inconventional constant on-time control with small ESR value on the output capacitor, theconverter is easily affected by the noise due to small output ripple, which is dominatedby the ripple on the output capacitor, the ripple compensation is required to guaranteethe stability of the system. The COT control does not have an internal clock in thesystem. Thus, the COT control should still keep a constant switching frequency at thecontinuous conduction mode (CCM) operation to ensure that the electromagneticinterference (EMI) can be minimized.Therefore, this thesis proposes a new programmable constant on-time (PCOT)control BUCK regulator structure can improve frequency variation in CCM and thusstabilize the system without being affected by the input voltage. And designed a newbandgap reference with good second-order temperature compensation feature, whichprovides a stable reference voltage for the system. The implementation of a zero currentdetector (ZCD) is the solution to enhance the efficiency in light load, and the systemoperates in the variable frequency modulation (VFM) state. Meanwhile, a variety ofprotection circuits are integrated to prevent system from being damaged during a faultcondition. Finally, some of sub-blocks have been simulated by using H-spice and Cadencebased on0.6μm16V HV-CD process, including constant on-time generation circuit,bandgap reference and zero current detector. And simulation of the working status ofthe system with different applications, the efficiency and load transient response of thechip were verified. The simulation results show that the switching frequency in CCMoperation is relatively constant over a wide input voltage range, which conform todesign requirements.