Batteries provide significantly more energy than supercapacitors, making them superior for applications requiring backup power over extended periods. The LTC4040 utilizes an integrated 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 functions as a buck battery charger for single-cell Li-Ion or LiFePO4 batteries, prioritizing system charging. When the input power drops below the adjustable PFI (Power-Fail Input) level, the LTC4040 acts as a boost regulator capable of supplying up to 2.5 A to the system output from the backup battery. In the event of a power failure, the device's PowerPath™ control provides reverse lockout and seamless switching between input and backup power. 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 power systems, and USB-powered devices.
The LTC4040 also includes optional overvoltage protection (OVP) to protect the IC from input voltages exceeding 60V using an external MOSFET. Its adjustable input current limiting function allows operation from a limited current source and prioritizes system charging current over battery charging current. An external disconnect switch isolates the primary system input power when the backup power is in operation. The LTC4040's 2.5A battery charger provides eight selectable and optimized charging voltages for Li-Ion and LiFePO4 batteries. The device also features input current monitoring, an input power loss indicator, and a system power loss indicator.
The LTC4040 is supplied in a low-profile (0.75mm) QFN package with 24 pins (4mm x 5mm) and a metal solder area on the back for excellent thermal performance. The device operates between -40°C and 125°C, for Grade E and Grade I applications.

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