Power Supply Design for Battery Systems on Embedded Systems Development

Buck Converters in Practice

Mon, 01 Jan 0001 00:00:00 +0000

Buck Converters in Practice#

A single lithium-ion cell delivers 4.2 V at full charge and sags to about 3.0 V at cutoff. Most MCU systems need a regulated 3.3 V rail, making the buck (step-down) converter the default topology for the upper portion of the discharge curve — from 4.2 V down to roughly 3.5 V, where the converter still maintains dropout headroom. Modern micro-buck ICs achieve 90–96 % efficiency in this range, draw sub-microamp quiescent currents in sleep, and fit in packages smaller than 2 mm × 2 mm. Selecting the right IC, inductor, and capacitors — and placing them correctly on the PCB — determines whether the system meets its efficiency, noise, and thermal targets.

Boost & Buck-Boost Topologies

Mon, 01 Jan 0001 00:00:00 +0000

Boost & Buck-Boost Topologies#

A single lithium-ion cell delivers 4.2 V at full charge but sags to 3.0 V — or lower under heavy load — at end of discharge. A buck converter regulating 3.3 V output loses regulation once the cell drops below roughly 3.5 V, discarding 15–20 % of the battery’s usable energy. Boost converters step voltage up, enabling operation from deeply discharged cells. Buck-boost converters handle both cases — seamlessly stepping down when the cell is above 3.3 V and stepping up when it drops below — extracting nearly the full capacity of the cell. Choosing between boost, buck-boost, and plain buck determines how much runtime the system can extract from a given battery.

Charge Pumps & Rail Generation

Mon, 01 Jan 0001 00:00:00 +0000

Charge Pumps & Rail Generation#

Not every rail in an embedded system needs an inductor-based converter. Charge pumps generate auxiliary voltages — doubled, inverted, or fractionally scaled — using only capacitors and switches. When current requirements are modest (under 100–200 mA) and magnetic EMI is a concern, charge pumps offer a smaller, quieter, and often cheaper alternative to inductors. Negative voltage rails for op-amp symmetric supplies, boosted rails for LED gate drivers, and bias voltages for MEMS sensors are classic charge-pump applications in battery-powered systems.

Power Sequencing — Multi-Rail

Mon, 01 Jan 0001 00:00:00 +0000

Power Sequencing — Multi-Rail#

Most embedded systems require more than one supply voltage. A typical Cortex-M7 design needs 1.8 V for the core, 3.3 V for I/O, and possibly 5 V for external peripherals. The order in which these rails turn on — and off — matters. Powering I/O pins before the core is ready can drive current into unpowered logic through ESD protection diodes, triggering latch-up. Removing core power while I/O rails remain active can force outputs into undefined states, back-driving connected devices. Power sequencing ensures every rail comes up and goes down in the correct order, with the correct timing, to prevent damage and undefined behavior.