Lowest-vIN CMOS Single-Inductor Boost Charger: Design, Limits, and Validation

The lowest input voltage for a single-inductor switched-inductor (SL) boost charger to draw power is critical for energy-harvesting applications. When a battery is fully discharged, the charger solely relies on the millivolt input-source voltage v
_S
to wake the system. When the charger is awake and operates in static mode, it needs to draw power from low voltage v
_S
efficiently. Thus, the major contribution of this article is theorizing the fundamental limits of SL converters, and experimentally validating the lowest v
_S
possible for a single-inductor boost to operate, both in wake and static mode. This article derives closed-form design expressions for all circuit components and validates the design theory with a 1.6-
μ
m CMOS prototype. When source resistance is 350 Ω, this prototype validates that the lowest-possible v
_S
for SLs in wake mode is 225–285 mV. In static mode, the lowest-possible v
_S
for SLs is 40 mV. Despite recent literature shows that switched-capacitors (SCs) can wake with lower v
_S
, theorizing and experimentally validating the lowest v
_S
possible for SL converters can prove the fundamental limits of SL chargers. Moreover, since this article also validates that SLs operate with lower v
_S
than SCs in static mode, thus, SC-SL hybrids are the best system.