14 March 2012

Power manager charges LiFePO4 cells at 3.5A

Linear Technology has introduced the LTC4156, 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 15W from a variety of sources while minimising power dissipation and easing thermal constraints. Its switching PowerPath topology 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.

According to Linear, because power is conserved, the LTC4156 allows the output load current to exceed the current drawn by the input supply, maximising use of the available power for battery charging without exceeding the input supply power delivery specifications.

As an example, when powered from a 5V/2A wall adapter, the ic's switching regulator is said to efficiently transfer more than 90% of the available 10W, enabling up to 2.4A charge current for faster charge times. Unlike ordinary switching battery chargers, Linear says 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 5V supply back to the USB port without any additional components.

A 2-wire I²C port is designed to provide broad adjustability for many system control parameters including charge current, input current (including USB 2.0 and 3.0 compatible settings) and float voltage (3.45/3.55/3.60/3.80V). 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 single cell LiFePO4 battery charger is capable of up to 3.5A charge current with 15 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 is said to prevent any damage from accidental application of high voltage. According to Linear, its diode controller guarantees that ample power is always available to VOUT even if input power is insufficient or absent. To minimise battery drain when a device is connected to a suspended USB port, an LDO from VBUS to VOUT provides the allowable USB suspend current to the application. To eliminate battery drain between manufacture and sale, a ship and store feature reduces the already low battery standby current to nearly zero.

The device compliments the LTC4155, which offers the same feature set for Li-Ion/Polymer battery-based systems. It is housed in a low profile (0.75mm) 28pin 4x5mm QFN package and is guaranteed for operation from -40 to 125°C.

Author
Linear technology

Supporting Information

Websites
http://www.linear.com/product/LTC4156

Companies
Linear Technology (UK) Ltd

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