40mA LDO with 15µA quiescent current — the battery-life spec
The MAX666CSA+ is a positive-output linear regulator delivering up to 40 mA from a 1.3 V to 16 V adjustable output, or a fixed 5 V option selected by pin-strapping. The headline number for a battery-powered design is the 15 µA quiescent current — the regulator's own draw stays under the self-discharge rate of a small lithium cell, so a sensor node that spends most of its life in sleep mode doesn't drain the battery between wake cycles.
Dropout and input range — what the rail needs
Maximum dropout is 0.9 V at the full 40 mA load — the input rail must stay at least 0.9 V above the target output across the full load range, or the output falls out of regulation.
Control features for the battery circuit
On-chip current limit protects the pass transistor and the load during a fault. The enable pin lets a microcontroller or a pushbutton gate the regulator — pulling it low drops the output and cuts the quiescent current to near zero. The low-battery detection comparator flags a falling input voltage before the regulator drops out, giving the system time for an orderly shutdown or a data save.
Analog Devices lists the MAX666CSA+ as Active with ROHS3 compliance.