An Ultralow-Power On-Die PMU in a 28-nm CMOS SoC With Direct Li-Ion Battery-Attach Capability

This paper introduces an on-die power management unit (PMU) within Blackghost 1.0—a test chip for Qualcomm’s newest Blackghost ultralow-power mixed-signal system-on-chip product family. Specifically targeted at battery-powered Internet-of-Things, wearables, and e-medical applications, Blackghost delivers unparalleled power efficiency through low-power innovations from software, architecture, and circuit design [Y. Pu et al., Proc. IEEE Symp. Low-Power High-Speed Chips (COOL CHIPS) , Apr. 2017, pp. 1–3]. It integrates a small footprint sensor/control processor based on ARM Cortex M0, an on-die PMU with direct Li-ion battery-attach capability, a computer vision classifier processor, a programmable DSP hardware accelerator, and an ultralow-power analog front end on a $3 \times 3$ mm 2 die in the TSMC 28LP CMOS process technology. The on-die PMU consists of a bandgap reference, a low-frequency RC clock, a high-frequency RC clock, a low drop-out linear regulator, and two switch mode power supply (SMPS) buck regulators. It supports direct Li-ion battery-attach by accepting input voltages up to 5 V. The total quiescent current of the entire PMU is only $9~\mu \text{A}$ . Its SMPS maintains high efficiencies (around 80%) with load currents as low as $10~\mu \text{A}$ .