The converter is typically 50% more efficient than existing converters at these current levels and is aimed at sensors for the Internet of Things and wearable designs.
"Typically, converters have a quiescent power, which is the power that they consume even when they're not providing any current to the load," says Arun Paidimarri at MTL when the work was done and now at IBM Research. "So, for example, if the quiescent power is a microamp, then even if the load pulls only a nanoamp, it's still going to consume a microamp of current. My converter is something that can maintain efficiency over a wide range of currents."The step-down converter takes input voltages ranging from 1.2 to 3.3 V with an output of 0.7 to 0.9 V.
"In the low-power regime, the way these power converters work, it's not based on a continuous flow of energy," said Paidimarri. "It's based on these packets of energy. You have these switches, and an inductor, and a capacitor in the power converter, and you basically turn on and off these switches."
The control circuitry for the switches includes a circuit that measures the output voltage of the converter. If the output voltage is below some threshold -- in this case, 0.9 volts -- the controllers throw a switch and release a packet of energy. Then they perform another measurement and, if necessary, release another packet.