L7983 is a 3 to 60V input 300mA output synchronous dc-dc converter from ST Microelectronics whose mode can be pin-selected to keep noise down or maximise efficiency at light load

ST-L7983-dcdc
The variable output variant can provide from 850mV to Vin.
Low noise operation is essential fixed frequency and low consumption operation is variable frequency, with single output pulses or bursts of pulses depending on load – see the data sheet for details.
Via two pins, an external resistor can set fixed frequency opertion to one of eight frequencies between 400kHz and 2.2MHz, with or without adding dither to spread the noise spectrum.

For other fixed operating frequencies, an external clock at 200kHz to 2MHz can be applied to the mode select pin.
In low consumption mode, no-load current can be as little as 10µA active, or 2.3µA when shut down.
Features include active dead-time control for the output transistors, soft-start, over-temperature protection, pulse-by-pulse current limiting (both transistors), over-voltage protection and adjustable input under-voltage lockout – the latter can be tuned to work with 12, 24 and 48V industrial bus standards.
An open collector output is provided through which to implement power-up voltage sequencing. The output voltage supervisor manages the reset phase for MCU or FPGA loads.
There are three variants
L7983PU33R with 3.3V fixed output voltage – eval board is STEVAL-L7983V33
L7983PU50R with 5.0V fixed output voltage – eval board is STEVAL-L7983V50
L7983PUR with adjustable output voltage – eval board is STEVAL-L7983ADJ
Packaging is 3mm x 3mm DFN10 package.
Applications, some battery-powered, are foreseen in industrial fail-safe systems, intelligent nodes, appliances, robotics and telecom equipment.