Buck DC/DC Converters with integrated battery voltage monitor

The Japanese company Ricoh Electronic Devices presented two new Buck converters with VFM mode; we are talking about the RP514 and RP515 models, designed for uses that require very low power consumption such as the IoT wearable devices.

Power saving and battery monitoring

One of the key features of the RP514 and RP515 models is the battery monitoring circuit. Generally, the input impedance of an A/D converter is low, resulting in a considerable flow of current to ground, which inevitably discharges the battery and reduces the life of the application. The RP514 and RP515 offer a simple solution with an integrated resistive divider and a voltage tracker, such as a buffer. This circuit has the advantage of having a much lower current flow to ground and the buffer output is compatible with the input impedance of the A/D converter. In addition, all essential components are integrated in the chip: this allows you to significantly reduce the footprint on the board and the associated costs. This makes it possible, for example, to create a simple charge indicator for the main batteries.

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Possible applications

Today's wearable and IoT devices mainly operate in sleep mode, so power consumption is basically defined by the quiescent current, which refers to the rest state of the circuit, without any output load. In this mode, the system is inactive, but ready to activate at any time to perform a task, transmitting data and then returning to the sleep mode. The RP514 and RP515 models have an extraordinarily low quiescence current and consume only 300 nA, thus extending battery life.

The difference between the two models lies in the output current capacity: RP514 is capable of delivering 100mA while RP515 delivers 300 mA. Both offer synchronous rectification and integrate transistor MOSFET for high and low-side driving. DC/DC converters operate in VFM mode, the best way to achieve high efficiency performance when the required output current is low; the resulting maximum efficiency is in the order of 95%.

“Under Voltage Lock Out” circuit is included, which is disabling the DC/DC Converter in case the input voltage drops below a minimum threshold. A soft-start circuit controls the output voltage to ramp-up with a constant slope, and prevents any output overshoot and undershoot during the start-up period.

The Lx current limit circuit prevents the peak current through the inductor to exceed a specific maximum current threshold.

Typical Applications of RP514 Series

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