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Buck DC/DC converters with ultra-low output voltage for wearables and IoT devices

Ricoh Electronic Devices has launched two buck DC/DC converters for use in wearable devices and applications for Internet of Things extending battery life, reducing mounting area and weight on high density boards.

Wearable and IoT devices operate mainly in a sleep mode and power consumption is significantly defined by the quiescent current, referring to a circuit’s quiet state, not driving any load. In this mode, the system is idle but ready to wake up at any time to perform a task, transmitting some data and resume to sleep mode again.

The RP516 and RP517 have been optimised to prolong battery life and have been designed for applications that require a low supply voltage in between 0.3 and 1.2 V. This kind of power supply is tailored to support the newest generation of low power MCU’s, GPS/GNSS receiver/processors and other ICs which are required in IoT applications for a low power wireless sensor network and wearable devices.

The DC/DC converters operate in a VFM mode and the efficiency at light loads in particular was considerably improved and has a peak at 75%, even at 0.01 mA output current an efficiency performance of about 67% is achieved (conditions: Vout=0.5V, Vin=1.8V).

The low quiescent current of only 300 nA contributes to extend battery life and makes it possible for the designer to select a smaller sized battery for the application.

The main difference between the two products is their output current power; they deliver 100 and 300 mA respectively. Both products offer synchronous rectification and have high and low side MOSFET driver transistors embedded. Three different packages are available: A standard SOT-89-5, leadless DFN2527-10 or the most compact WLCSP-8-P1 package. By using the proposed external components, it takes up only 8.3 mm2 of printed circuit board area. Thanks to the wide input voltage range, the two DC/DC Converters are able to operate from various power supplies like a USB port, a single cell Li-Ion and other regular batteries.

Protection circuits are integrated: An Under Voltage Lock-Out circuit 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 smoothly, preventing 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.

The RP516 and RP517 have an optional auto-discharge function; this feature rapidly discharges the output capacitor once the CE pin disables the chip.

Neil Tyler

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