Why do you need a voltage regulator when operating from a battery?
The battery output voltage goes down over time, so you need a regulator to maintain the required system voltage. Also, the device must provide tight output voltage regulation as battery voltage decreases.
Why would you need a step-down (buck) regulator for a battery-powered application?
IC operating voltages are decreasing relative to battery output voltages. A single Li-ion battery output can reach 4.2 V, and three new alkaline cells can produce 4.5 V. Typical required IC operating voltages are often about 3.3 V and heading lower toward 1 V, so the buck regulator is necessary.
Why use a switch-mode voltage regulator for battery-powered systems?
The switch-mode regulator can provide efficiencies of 90% or greater. In contrast, the linear low-dropout (LDO) regulator usually exhibits only 50% to 60% efficiency. Higher efficiency means longer battery run time.
What are the requirements for voltage regulators in battery-powered systems?
The voltage-regulator IC should require very few low-cost, external components. To minimize size and weight, it should be housed in a small-outline package. Also, to minimize the size and weight of its associated surface-mount capacitors and inductors, a switch-mode regulator should operate at its highest usable switching frequency.