Regenerative Breaking: Optimal Energy Recycling for Energy Minimization in Duty-Cycled Domains

• Published in: IEEE journal of solid-state circuits Vol. 58; no. 1; pp. 1 - 10
• Main Authors: Huang, Chi-Hsiang, Mandal, Arindam, Pena-Colaiocco, Diego, Silva, Edevaldo Pereira Da, Sathe, Visvesh S.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.01.2023; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Buck converters; Computer architecture; DC–DC converter; Decoupling; Discharges (electric); Domains; Energy; energy-autonomous integrated systems; Internal energy; Internet of Things; Internet of Things (IoT); Leakage; Loss measurement; Microprocessors; Optimization; power delivery; Power flow; Recycling; run-time optimization; Steady-state; System on chip; wearable electronics
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/JSSC.2022.3221143

The system on chip (SoC) domains in wearable and Internet-of-Things (IoT) applications are frequently duty-cycled, placed in a power-gated () mode, and woken up for brief periods to perform tasks (mode). Duty cycling reduces steady-state leakage energy loss, but the significant quantity of energy stored in the domain decoupling capacitor () at the onset of mode is discharged through domain leakage. This energy overhead significantly degrades overall system efficiency. This article presents an architecture that efficiently reverses power flow in a buck converter at the onset of to recycle the stored energy stored in before, thus minimizing transient leakage losses (). A fully digital run-time optimizer is presented to achieve optimal recycling and demonstrated in a voltage domain consisting of a duty-cycled, buck-regulated ARM M0 processor. Measurements indicate that 59.4% reduction is achieved with 3.2-ms duration. These savings translate to total system energy savings of 56.6% for a duty-cycled processor executing 5k cycles during the operation.