A Scalable Single-Inductor Multiple-Output DC-DC Converter With Constant Charge-Transfer and Power-Up Sequencing for IoT Applications

This paper presents a single-inductor, multiple-output (SIMO) DC-DC converter suitable for the micro-battery-powered IoT (Internet-of-Things) applications operating with a very low activity factor. Targeting an average output power of few mu W with a peak output power requirement of a few mW in each output channel, the proposed converter transfers constant-charge to its outputs in a complete switching cycle. Multiple IoT nodes are serviced in a time-division multiplexing under discontinuous conduction mode (DCM) of operation for minimizing the cross-regulation issue. An internal priority sequencing logic ensures reliable power-up sequencing during startup. Additionally, the proposed SIMO converter offers an inherent soft-start mechanism, effectively mitigating current-stress on power MOSFETs. Also, the features of priority-based servicing under dynamic conditions, resolve a conflict when catering to multiple outputs at the same instant. The design is highly scalable towards meeting the increased load demand. Implemented in a standard 180 nm CMOS technology, the proposed converter generates three outputs (0.9 V, 1.2 V and 1.5 V) with a maximum load current of 5 mA simultaneously in each of the output channels. Using a single inductor of 10 mu H and an output capacitor of 10 mu F in each of the outputs, the proposed converter shows an output ripple < 22 mV with a peak power efficiency of 91.73 %