Dual input prioritiser provides low backup solution
Analog Devices, which recently acquired Linear Technology, has announced the LTC4418, a dual input power prioritiser for 2.5-40V 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 LTC4418 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 LTC4418 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 the LTC4418 suitable for portable battery-operated systems.
Unlike diode-based solutions, the LTC4418 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 minimising 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.