A low power digital controller for DC-DC converter applications with integrated PFM mode detector

Switching Converters (SC) are an excellent choice for hand held devices due to their high power conversion efficiency. However, they suffer from two major drawbacks. The first drawback is that their dynamic response is sensitive to variations in inductor (L) and capacitor (C) values. A cost effective solution is implemented by designing a programmable digital controller. Despite variations in L and C values, the target dynamic response can be achieved by computing and programming the filter coefficients for a particular L and C. Besides, digital controllers have higher immunity to environmental changes such as temperature and aging of components. The second drawback of SCs is their poor efficiency during low load conditions if operated in Pulse Width Modulation (PWM) mode. However, if operated in Pulse Frequency Modulation (PFM) mode, better efficiency numbers can be achieved. A mostly-digital way of detecting PFM mode is implemented. Besides, a slow serial interface to program the chip, and a high speed serial interface to characterize mixed signal blocks as well as to ship data in or out for debug purposes are designed. The chip is taped out in 0.18µm IBM's radiation hardened CMOS process technology. A test board is built with the chip, external power FETs and driver IC. At the time of this writing, PWM operation, PFM detection, transitions between PWM and PFM, and both serial interfaces are validated on the test board.