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Buck Regulator Has Minuscule Quiescent Current, On-the-Fly Adjustable Output

Feb. 15, 2019
The ST1PS01 meets the needs of harvesting and battery-supplied applications, delivering up to 400 mA, while allowing users to dynamically select one of four output voltages via two digital control lines.

As the Internet of Things (IoT) and other applications increasingly embody functions with ultra-low duty cycles (think temperature sensing) while operating from severely limited energy sources (harvesting or 10-year batteries), low quiescent current is becoming a specification as important as actual operating current.

The ST1PS01 step-down (buck) dc-dc converter developed by STMicroelectronics (Fig. 1) features requisite small size and high efficiency, of course. It’s noteworthy for two other features: a quiescent-current value of 500 nA (typical), and its output voltage can be dynamically set to one of four values between 1.8 and 3.3 V via two digital-control inputs (the specific available four values depend on which ST1PS01 variant is ordered).

1. The STMicroelectronics ST1PS01 delivers up to 400 mA from a 1.14- × 1.41-mm flip-chip package, with quiescent current of just 500 nA and four digitally selectable output voltages that can be switched dynamically. 

Key applications include asset tracking, gas/water energy meters, and long-term portable medical monitoring, to cite a few among many others. The IC, complete with integrated power switch, synchronous rectifier, and integrated compensation network, has an input-voltage range between 1.8 and 5.5 V (the 1.8-V minimum supply-input voltage allows use of various battery chemistries including a single lithium-based cell). Maximum delivered output current is 400 mA.

Typical efficiency is 94% at 1 mA load with VIN at 3.6 V and VOUT at 3.3 V (Fig. 2), while output voltage accuracy measures ±2%. When in use, the IC requires just a small inductor, two same-value capacitors, and a resistor (typically 2.2 µH, 10 µF, and 1 MΩ, respectively).

2. Performance of the ST1PS01 is characterized by multiple graphs showing efficiency vs. load for VOUT = 1.8 V (left) and efficiency vs VIN, for VOUT = 1.8 V (right).

Other features include undervoltage lockout (at 1.57 V), embedded soft-start circuit, overcurrent protection, active output-voltage discharge, and an output-voltage power-good flag. Small size is also a feature thanks to its 1.14- × 1.41-mm flip-chip package with 400-μm pitch. Design-in support is provided by the STEVAL-1PS01EJR evaluation board. Available now, the ST1PS01, specified for ambient temperature operation from −40 to +85°C, is priced at $0.686 each (1000-piece lots).

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