Nanopower buck-boost DC/DC converter with energy-harvesting charger

June 30, 2014 // By Graham Prophet
LTC3331 is a complete energy harvesting solution that delivers up to 50 mA of continuous output current to extend battery life when harvestable energy is available.

A simple 10 mA shunt enables charging of a rechargeable battery with harvested energy while a low-battery disconnect function protects the battery from deep discharge. The LTC3331 requires only 200 nA of supply current from the battery when providing regulated power to the load from harvested energy and only 950 nA operating when powered from the battery under no-load conditions.

The device integrates a high voltage energy harvesting power supply, a battery charger, and a synchronous buck-boost DC/DC converter powered by a rechargeable battery, creating a single continuous regulated output for energy harvesting applications such as those in wireless sensor networks. The energy harvesting power supply, consisting of a full-wave bridge rectifier accommodating AC or DC inputs and a high efficiency buck converter, harvests energy from piezoelectric (AC), solar (DC), or magnetic (AC) sources. When harvested energy is not available, the rechargeable battery input powers a buck-boost converter that operates over the full battery voltage range up to 4.2V and can regulate whether the input is above, below or equal to the output. The LTC3331 automatically transitions to the battery when the harvesting source is no longer available.

The LTC3331's energy harvesting inputs operate from a voltage range of 3V to 19V AC or DC, making the device suitable for a wide array of piezoelectric, solar, or magnetic energy sources. Its input undervoltage lockout threshold settings are programmable between 3V and 18V, enabling the application to operate the energy harvesting source at its peak power transfer point. Other features include pin-programmable output voltages and buck-boost peak current limits, a supercapacitor balancer, and an input protective shunt (up to 25 mA at VIN ≥20V).

In a 5 x 5mm QFN package, pricing starts at $3.55 (1,000); an industrial temperature grade version, the LTC3331IUH, is also available at $3.90 (1,000).

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