The control system is responsible for the second important task of the DC-DC converter: Regulating the output voltage to the desired level. For the purpose of monolithic DC-DC converters a new set of challenges emerge, both in terms of the control strategy and the basic design of the control system. This is due to the requirement of high switching frequencies and short switching times, needed to guarantee the optimal performance of the monolithic DC-DC converter. Therefore, novel control strategies are proposed in this chapter. These discussions include the principle of the control strategies and the circuits used in the practical chip implementations discussed in this book. In this chapter the two conventional control strategies PWM and PFM are discussed and compared to each other in Sect. 5.1. The Constant On/Off-Time (COOT) control strategy, together with implementation examples for single-phase, single-output and multi-output converters, is explained in Sect. 5.2. The Semi-Constant On/Off-Time (SCOOT) control strategy, together with implementation examples for multi-phase and multiple-output converters, is explained in Sect. 5.3. The Feed-Forward Semi-Constant On/Off-Time (F2-SCOOT) control strategy, together with an implementation example, is discussed in Sect. 5.4. The aspect of start-up, in combination with some start-up circuit implementations, is discussed in Sect. 5.5. Finally, the chapter is concluded in Sect. 5.6.
KeywordsPulse Width Modulation Boost Converter Switching Cycle Buck Converter Pulse Frequency Modulation
- [Dei78]C. Deisch, Simple Switching Control Method Changes Power Converter into a Current Source, in IEEE Power Electronics Specialists Conference, 1978, pp. 300–306 Google Scholar
- [Ser07]B. Serneels, High Voltage Line Drivers for XDSL in Nanometer CMOS, PhD thesis, ESAT-MICAS, K.U. Leuven, Belgium, 2007 Google Scholar
- [Wen07]M. Wens, K. Cornelissens, M. Steyaert, A Fully-Integrated 0.18 μm CMOS DC-DC Step-Up Converter, Using a Bondwire Spiral Inductor, in IEEE Proceedings of the European Solid-State Circuits Conference, vol. 33, 2007, pp. 268–271 Google Scholar
- [Wen08a]M. Wens, M. Steyaert, A Fully-Integrated 0.18 μm CMOS DC-DC Step-Down Converter, Using a Bondwire Spiral Inductor, in IEEE Proceedings of the Custom Integrated Circuits Conference, vol. 30, 2008, pp. 17–20 Google Scholar
- [Wen08b]M. Wens, M. Steyaert, A Fully-Integrated 130 nm CMOS DC-DC Step-Down Converter, Regulated by a Constant On/Off-Time Control System, in IEEE Proceedings of the European Solid-State Circuits Conference, vol. 34, 2008, pp. 62–65 Google Scholar