A self-biased 5-to-60V input voltage and 25-to-1600µW integrated DC-DC buck converter with fully analog MPPT algorithm reaching up to 88% end-to-end efficiency

Energy harvesting is seen as an enabling technology for autonomous wireless sensing in automotive applications. This technology may rely on piezoelectric or electrostatic energy conversion using the energy available during the tire impact with the road. The power management system has to transfer harvested power to the load battery (few μW to mW) with the highest possible efficiency. An electrostatic harvester can generate voltages up to 40V even at low accelerations [1]. Hence, a high voltage (HV) DC-DC converter is needed to maximize the energy transfer from the harvester to the load battery. However, HV buck converters including maximum power point tracking (MPPT) algorithms have been shown only for much higher ranges of power, in the order of W [2]. On the other hand, all reported converters working in the sub-mW power range are not able to sustain high input voltages and do not include an integrated MPPT algorithm [3, 4]. Until this work, no solution in literature is able to interface with these electrostatic energy harvesters. Figure 4.6.1 shows the block diagram of the system, designed and fabricated in TSMC 0.25μm BCD CMOS (60V option). The IC is able to interface a vibrational harvester by means of few external components: a rectifier, its load capacitor C_IN, and an inductor L. The converter is consisting of a power train and its control circuits. The power train is implemented with the external inductor L, and the integrated power switches M_P and M_N. The integrated control circuits have to provide the correct gate voltages V_GN and V_GP for allowing the converter to maximize its output power. All circuits are biased by means of an integrated current reference and are supplied by the load battery voltage V_BAT and the DC input V_IN.