Dual input prioritizer offers low quiescent current backup supply switchover solution

Linear Technology’s LTC4418 is a dual input power prioritizer for 2.5V to 40V systems. To enable portability, preserve memory during brownouts, and ensure a graceful shutdown on power loss, electronic systems employ batteries and capacitors for backup power. The device normally powers the load from the higher priority main supply such as a wall adapter or main battery, switching to the backup supply - typically a battery or large value capacitor - during primary brownout or power loss conditions. With up to 40V operating capability, the device accommodates a wide range of power sources such as wall adapters, USB ports, supercapacitors, and multicell lead-acid, Li-Ion, or NiMH batteries. A low 26µA operating quiescent current and a shutdown mode make it ideal for portable battery-operated systems. Unlike diode-based solutions, the device does not require the backup supply voltage to be lower than the main voltage. External back-to-back P-channel MOSFET switches multiplex from the primary to the backup input when the primary goes out of the valid voltage window setup with adjustable and precise undervoltage and overvoltage thresholds. Carefully designed break-before-make fast switch control blocks reverse and cross conduction currents while minimizing output voltage droop. An external capacitor sets the time that a supply needs to stay within its voltage window before being considered valid. Reversed input voltages up to -42V are blocked, protecting the load. More than two supplies are prioritized by cascading any combination of LTC4418 and the triple-supply LTC4417. Specified over the 0C to 70C commercial and -40C to 85C industrial temperature ranges, the device is offered in a 20-lead 4mm x 4mm QFN package.