DC-DC converter integrates IoT battery monitor

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By Nick Flaherty

Ricoh Electronic Devices in Japan has launched a buck-boost DC-DC Converter with an integrated battery voltage monitor for IoT designs to measure the remaining charge left in the battery.

The RP605 is aimed at applications in the Internet of Things (IoT), wearable devices and wireless communications modules that need a low level of current consumption to extend battery life.

The additional battery monitor circuit avoids the need for an external resistor divider and MOSFET connected to an A to D converter. This typically has allow input impedance that leads to considerable current flow to ground, draining the battery and limiting the lifetime of the application.

The RP605 provides a simple solution with a built-in resistor divider and voltage follower as a buffer. This means there is much less current flow to ground and the output is compatible with the input impedance of the A to D converter.  The quiescent current of this circuit is only 100 nA and has an additional chip enable pin (CE2) instead of using a discrete MOSFET.

All the essential components for this circuit are integrated into the chip, reducing the footprint on the board for a simple fuel gauge for primary batteries in IoT designs.

The RP605 is particularly well suited when a supply voltage is required and located somewhere in between the voltage level of a fully charged and fully discharged battery. At a certain moment the DC-DC Converter switches over from Buck to Boost mode automatically in order to maintain the output voltage setting.

The RP605 is designed for applications that are mainly in sleep mode and wake-up periodically to perform a measurement, transmit data and then return to sleep mode. For this type of applications, the current consumption in sleep mode should remain as low as possible. The RP605 has an impressive low quiescent current and consumes only 300 nA (DC-DC Converter part), prolonging battery life or makes it possible for the designer to select a smaller sized battery for the application.

The RP605 is able to provide up to 300 mA in Buck mode whilst in Boost mode the output current is less and related to the input voltage level.

Multiple protection circuits are integrated, including an Under-Voltage Lock-Out circuit which disables 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 smoothly 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. An output overvoltage protection which turns off both the P-channel and N-channel MOSFETs and thermal protection, shutting down the IC in case the junction temperature increases above 140ºC.

The RP605 has an optional auto-discharge function, which rapidly discharges the output capacitor once the chip is disabled by the CE pin.

The parts are available in chip scale WLCSP-20-P3 and DFN(PLP)2730-12 packages.



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