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4A multicell/chemistry battery charger controllers

Linear Technology has introduced the LTC4012, LTC4012-1 and LTC4012-2 fast-charge 4A capable high efficiency switchmode battery charger controllers for multiple battery chemistries. The LTC4012 supports Li-ion/Polymer, NiMH, NiCd and sealed lead acid battery chemistries in single and multicell configurations. The LTC4012 offers an adjustable battery termination voltage, while the LTC4012-1 and LTC4012-2 utilise a programmable internal resistor divider to charge from 1 to 4 series Lithium cells at multiples of 4.1V and 4.2V, respectively. All devices feature a wide output voltage range of 2V to 28V. The devices' analogue INFET control eliminates the need for an external blocking diode at the power input, thereby increasing efficiency and reducing the solution footprint. Also, AC adapter current limiting maximises the charge rate for a given fixed input power level, allowing the end-product to operate at the same time the battery is charging without complex load management algorithms. The ICs operate at input voltages from 5V to 28V and are intended for applications including portable computers, portable instruments, and battery backup systems.

The controller’s synchronously rectified, buck switching topology drives all N-channel MOSFETs and enables efficiencies more than 90% at 3A. Final float voltage accuracy is specified at ±0.5% and charge current is programmable with an accuracy of ±4%. The ICs quasi-constant frequency PWM architecture assures no audible noise operation and minimises filtering needs, while the high 550kHz operating frequency allows the use of small inductors and capacitors. Improved non-overlap control keeps efficiency high as external power FET turn-on/off times may vary with temperature and supplier. The contollers consume less than 30uA without a DC power input, increasing battery run time in portable applications. For safety and autonomous charge control, the ICs include battery float voltage over-voltage protection, reverse charge current protection, charge current monitoring, soft start, AC adapter present indication, and current limit indication. The LTC4012/-1/-2 are housed in a compact 20-lead, low-profile (0.75mm) 4x4mm QFN package. They operate from 0°C to +85°C ambient temperature.