The device is designed to operate with an input voltage supply range between 2.5 V and 5.5 V. This input supply can be generated from a single cell Li-Ion battery, two primary cells or a regulated pre-regulator. The voltage headroom required for each of the PMIC regulators must be taken into account when defining selecting the supply voltage. For example, if the Bucks require 700 mV head room and the output voltage is configured as 3.3V, then the input supply must be at least 4 V to allow sufficient headroom. The resistance of the input supply rail must be low enough that the input current transient does not cause too high drop in the device supply voltage that can cause false UVLO fault triggering. If the input supply is located more than a few inches from the device, additional bulk capacitance may be required in addition to the ceramic bypass capacitors. An electrolytic capacitor with a value of 47 μF is a typical choice. When using a pre-regulator to supply the PMIC, it is recommended to select the pre-regulator without active discharge to hold the voltage at the input of the PMIC for as long as possible during a uncontrolled power-down.