Power Supply Design for Battery Systems#

A lithium-ion cell delivers a voltage that slides from 4.2V at full charge down to 3.0V (or lower) at cutoff. Most MCUs and peripherals need a stable 3.3V, 1.8V, or both — and some subsystems (LED drivers, motor controllers, RS-485 transceivers) need 5V or higher. The regulator topology that bridges the gap between a sagging battery rail and a stable output determines system efficiency, thermal performance, and ultimately runtime.

Buck converters handle the 4.2V→3.3V case efficiently but lose regulation as the cell drops below 3.3V. Buck-boost converters maintain output across the full discharge range at the cost of added complexity and slightly lower peak efficiency. Charge pumps generate auxiliary rails without inductors. Multi-rail systems require sequencing to avoid latch-up and contention. This section covers the practical converter selection, layout, and sequencing patterns that connect a battery cell to stable, clean power rails.

What This Section Covers#

• Buck Converters in Practice — TPS62802, AP3429, and similar micro-buck ICs: efficiency curves, inductor/capacitor selection, and layout for battery-to-3.3V conversion.
• Boost & Buck-Boost Topologies — TPS63001, TPS61200, and maintaining stable output as a Li-Ion cell sags from 4.2V to 3.0V.
• Charge Pumps & Rail Generation — Negative rails, voltage doubling, and inductorless topologies for LED drivers and op-amp supplies.
• Power Sequencing — Multi-Rail — Enable-chain sequencing, GPIO-controlled enables, and timing requirements for 1.8/3.3/5V multi-rail systems.