Battery Charger Minimises Power Dissipation

Linear Technology has introduced the LT3651-4.2, a 4A monolithic synchronous buck battery charger for one-cell li-ion/polymer batteries used in industrial hand-held instruments and notebook computers. The LT3651-4.2 accepts inputs up to 32V with a 40V absolute maximum rating for added system margin. Charge current is programmable and dynamically adjustable up to 4A; fully integrated synchronous power devices minimise power dissipation and save board space.

User-selectable timer or C/10 termination requires no external microcontroller and simplifies the design. The LT3651-4.2 does not require external high-precision resistors to set the float voltage, further saving cost and space. Applications include industrial hand-held instruments, 12V to 24V automotive and heavy equipment applications, desktop cradle chargers and notebook or tablet computers. The programmable switching frequency (200kHz to 1MHz) of the LT3651-4.2 enables the designer to balance solution size, power loss and filtering needs.

Synchronous operation enables charging efficiencies as high as 90 per cent. Final float voltage accuracy is +0.5 per cent, charge current accuracy is +7.5 per cent and C/10 detection accuracy is +4 per cent. Once charging is terminated, the LT3651-4.2 automatically enters a low current standby mode, which reduces the input supply current to 80uA. In shutdown the input bias current is reduced to 15uA. The LT3651-4.2 maximises battery life during all non-charging periods by draining <1uA from the battery. For safety and autonomous charge control, the device includes: automatic restart and preconditioning; a thermistor input for temperature-qualified charging; programmable input current limit; bad battery detection; and binary-coded status-output pins.

The LT3651-4.2 is available in a low-profile (0.75mm) 36-pin 5 x 6mm QFN package, and is offered in both E and I grade versions, guaranteed from -40C to 125C. Pricing starts at $4.13 and $4.75 each, respectively, in 1,000-piece quantities. Two-cell 8.2V and 8.4V options and a one-cell 4.1V version are planned for release within the next few months.

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