Choosing the Right Step-Up/Down Voltage Regulator for Portable Applications
Introduction
A popular power source for portable devices is a single lithium-ion cell with 4.2V at full charge and 2.8V at end of discharge. However, some functions within portable electronics, such as a SIM card and DSP, require 2.8V and 3.3V. These are normally provided by low noise LDOs. The LDOs inputs (VCC) must be at a slightly higher voltage than the highest LDO output. Hence, VCC ends up right in the middle of the lithium-ion battery’s range of operation. The use of a step-up/ down voltage regulator, capable of operating from an input that can be higher or lower than the output, becomes necessary.