15-W I2C power manager charges Li-Ion cells at 3.5-A for tablets, UMPCs and portable power systems

June 16, 2011 // By Paul Buckley
Linear Technology Corporation has introduced a high power, I2C controlled, high efficiency PowerPath manager, ideal diode controller and lithium-ion battery charger for single-cell portable devices such as tablet PCs, ultra-mobile PCs (UMPCs), personal video players, smart phones, digital cameras, PDAs, portable medical and industrial devices and personal navigation devices.

The LTC4155 is designed to efficiently transfer up to 15 W from a variety of sources while minimizing power dissipation and easing thermal budgeting constraints. The LTC4155’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 lithium-ion battery while preferentially providing power to the system load when input power is limited.

Because power is conserved, the LTC4155 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 and resulting in faster charge times. Unlike ordinary switching battery chargers, the LTC4155 features instant-on operation to ensure that system power is available at plug-in even with a deeply discharged battery. USB 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. The communications bus also allows the LTC4155 to provide status information such as battery temperature, input supply status, charger status and fault status.

The LTC4155’s autonomous full-featured single-cell Li-Ion/Polymer battery charger is capable of up to 3.5 A charge current and features four float voltage settings and fifteen charge current settings. For improved safety margin, an integrated overtemperature battery conditioning circuit can optionally reduce the battery voltage in case both high battery temperature and high battery voltage occur simultaneously.  The charger includes automatic recharge, bad cell detection, trickle charge, programmable safety timer, thermistor temperature qualified charging, programmable end-of-charge indication/termination and programmable interrupt generation.

The LTC4155’s dual input, priority multiplexing overvoltage protection