There might be one or two that create a suitable rail for the top mosfet using a bootstrap circuit, but these cease to work at either 0% or 100% duty-cycle, and sadly this is just the kind of operation that one might be using a MCU to achieve – after all, if you want a simple dc-dc, just us a chip.

And plenty of those dc-dc chips include internal mosfets will work with a 3V, or even 2V, input – they have nice driver-mosfet combinations squirrelled away that are inaccessible to the outside world and can not therefore be used as output stages for the 3V microcontroller I am postulating.

Enter a chip made by Rohm as part of a rather novel low-Iq buck-boost dc-dc for automotive use.

The chip, the BD90302NUF-C, includes a p-channel mosfet (55 mΩ typ), and n-channel mosfet (65 mΩ typ), and a driver for each, all powered by its own output voltage. Input currents can be up to 2A, switched at up to 2.4MHz.

It accepts a single input pwm, and has 10ns of shoot-through included between the two mosfets.

It looks to me that it will only work in boost circuits, which limits it to making between 3 and 5.5V from a lower voltage.

This could be vary handy for, for example, feeding a power led from a 2.5V supercapacitor, with the microcontroller getting its rail from the led forward voltage.

That said, few good leds drop as much as 3V today, so fingers crossed the chip would function at 2.8V.

And it might be a little tricky getting voltage onto the output pin to kick-start the circuit.

And I might have mis-read the whole thing…..

Nice one Rohm.