15-W I2C power manager charges LiFePO4 cells at 3.5-A for high power density portable and battery back-up systems

March 15, 2012 // By Paul Buckley
Linear Technology Corporation has introduced a high power, I2C controlled, high efficiency PowerPath manager, ideal diode controller and Lithium Iron Phosphate (LiFePO4) battery charger for single-cell devices such as portable medical and industrial devices, backup devices and other high power density battery-powered applications.

The IC is designed to efficiently transfer up to 15 W from a variety of sources while minimizing power dissipation and easing thermal constraints. The LTC4156's switching PowerPath topology seamlessly manages power distribution from two input sources such as a wall adapter and USB port to the device's rechargeable LiFePO4 battery while preferentially providing power to the system load when input power is limited.     

Because power is conserved, the LTC4156 allows the output load current to exceed the current drawn by the input supply, maximizing use of the available power for battery charging without exceeding the input supply power delivery specifications. For example, when powered from a 5-V/2-A wall adapter, the IC's switching regulator efficiently transfers over 90% of the available 10 W, enabling up to 2.4 A charge current for faster charge times. Unlike ordinary switching battery chargers, the LTC4156 features instant-on operation to ensure that system power is available at plug-in even with a deeply discharged battery. USB OTG (On-the-Go) support provides a 5 V supply back to the USB port without any additional components.     

A simple 2-wire I2C port provides broad adjustability for many system control parameters including charge current, input current (including USB 2.0 and 3.0 compatible settings) and float voltage (3.45 V/3.55 V/3.60 V/3.80 V). The communications bus also allows the LTC4156 to provide status information such as battery temperature, input supply status, charger status and fault status.     

The LTC4156's autonomous full-featured single-cell LiFePO4 battery charger is capable of up to 3.5 A charge current with fifteen charge current settings. The charger includes automatic recharge, bad cell detection, programmable safety timer, thermistor temperature qualified charging, programmable end-of-charge indication/termination and programmable interrupt generation.     

The LTC4156's dual input, priority multiplexing overvoltage protection (OVP) circuit prevents any damage from accidental application of high voltage. The device's ideal diode controller guarantees that ample power is always available to V OUT even if input power is