Control Techniques for Power Converters with Integrated Circuit

There have been many DC-DC power converters which are utilized in portable electronic devices, such as cellular phones and laptop computers, which are primarily supplied with power by batteries or adapters, regardless of the switching power converters or the linear power converters. For development trend of the power converters of integrated circuit, those designed to reduce standby power loss, feature well load regulation, fast load transient response, and high efficiency due to system design. A brief review of the pulse width modulation control mode and the pulse frequency modulation control mode of integrated circuit will be given in this chapter. This chapter would help readers to have a good overall view and appreciate the material in later chapter.

Two types of the conventional fixed-frequency pulse width modulated control circuits based on connection form are typically used, namely, voltage-mode control circuit and current-mode control circuit. For power converters of integrated circuit, it is commonly used with the current-mode control circuit instead of the voltage-mode control circuit, because the current-mode control circuit has a voltage feedback loop in addition to a current feedback loop, so it has faster transient response than the voltage-mode control circuit. This chapter will be compared between voltage-mode control circuit and current-mode control circuit. A well compensation design is the most important to increase the load transient response for switching converters of integrated circuit, so the different types of compensation design will also be given in this chapter.

Current-mode control circuit is widely used to achieve better transient response, because the current-mode control circuit contains two feedback signals for a voltage loop and a current loop. A difference between the voltage-mode control circuit and current-mode control circuit, the current-mode control circuit can sense the inductor current signal which causes the control to have a better transient response. However, it also produces a subharmonic issue when the duty cycle is larger than 50%. Designing a dynamic ramp with invariant inductor in current-mode control circuit for buck converter is showed in this chapter. This configuration maintains system stability under a wide range of the input/output voltages without changing the inductor and compensation circuit. The dynamic ramp can be adjusted according to varied the output voltage or the voltage droop between the input voltage and the output voltage to maintain bandwidth and phase margin using the invariant inductor and compensation circuit. Finally, 14-V input voltage, 12-V output voltage, and 24-W output power with the dynamic ramp sampling the output voltage is implemented using MathCAD predictions, SIMPLIS simulation results, and experimental results to verify its viability and superiority.

Many novel control circuits, such as central processing unit and electronic devices, have been reported for power supplies to meet stringent requirements in recent years. These devices can reduce standby power loss and increase the load transient response to achieve high performance and low loss of system design. Owing to the rapid development of microprocessors, over a billion transistors have been integrated into one processor. The power converter must be able to regulate its output voltage to be near constant as the load current demand varies anywhere from zero to full load, even when the change occurs in a relatively short time. A good performance of load transient response can save on output capacitor size and cost. Meanwhile, settling time and stability can be displayed in the load transient response, so power converter performance must be tested. Based on these requirements, the conventional constant on-time control circuit is widely used in central processing unit applications and other electronic devices with high slew rates because of the advantages of faster load transient response and better light-load efficiency compared with the current-mode control circuit. However, the on-time generator circuit of the conventional constant on-time control circuit can generate the fixed on-time width to control the driver circuit and achieve the voltage regulation if the conventional constant on-time control circuit wants to regulate a high VOUT and an increase in switching loss occurs, so this chapter is showed to compare different types of control circuit for buck converter like conventional constant on-time control circuit for buck converter, adaptive on-time control circuits for buck converter, ripple-based adaptive on-time control circuit with virtual inductor current ripple for buck converter, and current-mode adaptive on-time control circuit for buck converter.

The conventional fixed-frequency pulse width modulated control scheme for power converters is commonly used with current-mode control circuit instead of voltage-mode control circuit. However, adaptive on-time control circuits can achieve a faster transient response than the pulse width modulated control scheme because the former uses a comparator to control the on-time generator without an error amplifier. Thus, adaptive on-time control circuits do not exhibit system loop delay from the error amplifier. However, adaptive on-time control circuits do not meet the requirements of output equipment or devices to achieve a faster transient response. This chapter shows that adaptive on-time control circuits with a quick dynamic response can achieve a faster transient response than those without a quick dynamic response for buck converters. Implementing a quick dynamic response with constant frequency on-time control circuit for buck converter is showed in this chapter. The concept uses the quick dynamic response to filter V_out at the load transient to change the on-time width dynamically, preventing V_out from dropping markedly. Finally, 12 V input voltage, 3.3 V output voltage, and 60 W output power with a quick dynamic response are implemented to achieve afast load transient response for the integrated circuit of the proposed constant frequency constant on-time control circuit for buck converter. Experimental and SIMPLIS simulation results are compared to verify the viability and superiority of the proposed approach

Ceramic capacitors are highly suitable and preferred for lots power converter applications, such as digital cameras, netbooks, smartphones, and tablet computers due to their small size, low output voltage ripple, and high reliability requirements. The ESR of ceramic capacitors is substantially lower than that of tantalum equivalents. A low ESR prevents overheating of the device and circuit, thus increasing the overall reliability. However, ceramic capacitors contain a small output voltage ripple with a low ESR which may result in subharmonic oscillations for constant frequency on-time control circuit, so it is a design challenge. A quick dynamic response of ripple-based constant frequency on-time control circuit with virtual inductor current ripple for buck converter is showed in this chapter. The concept uses the capacitor and the resistor in a series to filter out the output voltage at load transient to dynamically change the width of on-time to prevent the V _OUT from dropping markedly. Finally, 12-V input voltage, 3.3-V output voltage, and 60-W output power with the quick dynamic response for the integrated circuit of the proposed buck converter are implemented to verify its viability and superiority.

In recent years, over one billion transistors have been integrated in one processor, core static current has been increased from 20 to 100 A, and core voltage has been reduced from 2 to 0.7 V. It is a challenge to provide the large output loading requirement for central processing unit application. Single-phase voltage regulator can be widely used in low-voltage converter applications with an output loading of up to approximately 25 A. However, power dissipation, power stress of the components, and efficiency become an issue under a large output load current. The benefits of using multiphase voltage regulators versus single-phase voltage regulator and the value of multiphase voltage regulators become evident when they are implemented. On the other hand, switching power supply requirement has the trend of fast transient response, because it can improve load transient response to reduce output capacitance, especially to central processing unit and high current slew rate load applications, so a pure constant current ripple on-time control circuit for voltage regulators cannot achieve a faster load transient response. Improved transient response using quick dynamic response of the constant current ripple on-time control circuit with native adaptive voltage positioning design for voltage regulators is showed in this chapter. The concept uses the quick dynamic response to filter V _OUT at the load transient to change the on-time width dynamically, preventing V _OUT from dropping markedly. This quick dynamic response does not need an extra pin to achieve a faster load transient response. Finally, the multiphase voltage regulator with the quick dynamic response of the constant current ripple on-time control circuit for the integrated circuit is implemented by experiment and simulation results to verify their viability and superiority.