Electronic Design

4-A Multi-cell Battery-Charger Controllers Require No Blocking Diode

The LTC4012, LTC4012-1, and LTC4012-2 fast-charge switch-mode battery-charger controllers from Linear Technology target multiple battery chemistries. The LTC4012 supports Li-ion/polymer (lithium-ion), nickel-metal-hydride (NiMH), nickel-cadmium (NiCd), and sealed lead-acid battery chemistries in single-cell and multi-cell configurations. It also offers an adjustable battery termination voltage, while the LTC4012-1 and LTC4012-2 use a programmable internal resistor divider to charge from one to four series lithium cells at multiples of 4.1 and 4.2 V, respectively.

Capable of 4 A, these devices feature a 2- to 28-V output voltage range. With their INFET control, there’s no need for an external blocking diode at the power input. This increases efficiency and reduces the solution footprint. Also, ac adapter current limiting maximizes the charge rate for a given fixed input power level, allowing the end product to operate while the battery is charging without complex load management algorithms. The ICs operate at input voltages from 5 to 28 V and suit portable computers, portable instruments, battery backup systems, and other applications.

The synchronously rectified buck-switching topology drives all n-channel MOSFETs and enables efficiencies greater than 90% at 3 A. Final float voltage accuracy is specified at ±0.5%, and charge current is programmable with an accuracy of ±4%. The quasi-constant frequency pulse-width modulation (PWM) architecture guarantees no audible noise operation and minimizes filtering needs, while the 550-kHz operating frequency allows the use of small inductors and capacitors.

Improved non-overlap control keeps efficiency high as external FET turn-on/off times may vary with temperature and supplier. The devices consume less than 30 µA without a dc power input, increasing battery runtime in portable applications. For safety and autonomous charge control, they include battery float overvoltage protection, reverse charge current protection, charge current monitoring, soft start, ac adapter present indication, and current limit indication.

The ICs come in a compact 20-lead, low-profile (0.75 mm), 4- by 4-mm quad flat no-lead (QFN) package. They’re guaranteed for operation from 0°C to 85°C ambient temperature. Pricing starts at $3.15 for the LTC4012 and $3.25 for the LTC4012-1 and LTC4012-2, all in 1000-piece quantities.

Linear Technology

www.linear.com

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