To the last Coulomb

Optimal battery use in mobile devices

Battery life is an important ergonomic factor when using mobile devices, since no-one likes to frequently hunt for a mains socket. When designing the devices, efficient use of battery energy must be guaranteed. This requires converters which can switch between buck & boost operations, as the cell voltage of the rechargeable battery and the supply voltage are often very close and sometimes require downward (at the beginning of the discharge) or upward conversions (towards the end). This provides the only possibility to fully use the energy provided by the battery. Ricoh Semiconductor, known for their extremely energy-efficient converters, regulators and RTCs, have launched new components for this field of application.

The RP600 multi converter

The RP600 can be powered by one or two alkaline batteries, by one NiMH battery or with a single cell LiIon battery. The voltages from these power sources can be converted and controlled to suit the supplied electronics. This new versatile product can be used in a variety of applications, e.g. as buck-boost circuit with a step-up converter and a serial voltage controller. This configuration is particularly helpful if the input voltage is below and above the desired output voltage. Battery life is enhanced since the battery is able to supply sufficient power even when the voltage is decreasing during the discharging process. The RP600 can also output 2 different voltages from a single input voltage, with one of the outputs above and the other below the input voltage. This means that two different circuits can be supplied from the same source.

Finally, the RP600 also permits “harvesting” or saving energy. The step-up DC/DC converter charges a large capacitor and is switched off by the voltage detector when charging is complete. The LDO, together with the capacitor, is operated in ECO mode in order to reduce energy consumption and supplies the required voltage to the circuit. Once the capacitor voltage falls below a defined value, the DC/DC converter starts charging again. This feature can be used in solar-powered applications or to lower the power consumption of wireless smoke detectors.

The DC/DC converter starts operation once the input voltage reaches 0.8 V; the RP600 operates in low-boost mode during the starting phase at 200 kHz as long as the output voltage is below 1.94 V. Once 1.94 V are exceeded, the RP600 switches to normal operation with a switching frequency of 1.2 MHz.

Further operation modes

The mode pin is used to operate the DC/DC converter either in fixed PWM mode or in the variable PWM/VFM mode, depending on the required output voltage. Automatic switching provides for high efficiency at low and high output currents. The voltage controller also offers two operating modes - it can either work in fast-transient mode or in ECO mode with particularly low power consumption, depending on the RP600 version. The voltage detector of the RP600 operates independently of other circuit components an can be used to monitor the DC/DC converter or the voltage controller or any external voltage.

The RP600 is available in a 10-pin DFN(PLP)2527-10 package which is particularly suited for densely packed and small circuit boards.

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