The LTC4040 is a complete lithium battery backup power management system for 3.5V to 5V supply rails that must be kept active during a main power failure. Batteries provide considerably more energy than supercapacitors, making them superior for applications which require backup for extended periods of time. The LTC4040 uses an on-chip bidirectional synchronous converter to provide high efficiency battery charging as well as high current, high efficiency backup power. When external power is available, the device operates as a step-down battery charger for single-cell Li-Ion or Lithium iron phosphate batteries while giving preference to the system load. When the input supply drops below the adjustable Power-Fail Input or PFI threshold, the LTC4040 operates as a step-up regulator capable of delivering up to 2.5A to the system output from the backup battery. During a power fail event, the device’s PowerPath™ control provides reverse blocking and a seamless switchover between input power and backup power. If there is a glitch on the power rail, the LTC4040 can also supply power from the battery to ensure seamless power delivery to the load. Only one inductor is required, saving space and complexity. The LTC4040 also includes optional overvoltage protection (OVP) which protects the IC from input voltages greater than 60V with an external FET. Its adjustable input current limit function enables operation from a current limited source while prioritizing system load current over battery charge current. An external disconnect switch isolates the primary input supply from the system during backup. The LTC4040’s 2.5A battery charger provides 8 selectable charge voltages optimized for Li-Ion and lithium iron phosphate batteries. The device also includes input current monitoring, an input power loss indicator and a system power loss indicator. The LTC4040 is housed in a low profile 24-pin 4mm x 5mm QFN package with backside metal pad for excellent thermal performance. Typical applications for the LTC4040 include fleet and asset tracking, automotive GPS data loggers, automotive telematics systems, toll collection systems, security systems, communications systems, industrial backup and USB-powered devices.