SUPPLY CHAIN
Ultralow Quiescent Current The buck converter’s quiescent current is especially important since the device is in deep sleep or quiet mode most of the time,
consuming only 100µA or less. With VOUT = 1.8V, the output power during deep sleep is
POUT = 1.8V × 100µA = 180µW. With η = 90%, the input power is:
If the buck converter is not carefully chosen and has a typical quiescent current of 3µA and a 3.6V input voltage, there is an additional power dissipation of:
The final buck converter efficiency is:
A quiescent current of 3µA robs the buck converter of 4 efficiency points, draining the battery significantly faster!
On the other hand, a buck converter with 300nA quiescent current will barely reduce the efficiency, lowering it by only half a percentage point. For asset tracking applications, it is critical to select a buck converter with ultralow quiescent current as the system spends the majority of the time in quiet mode and relies on a battery.
Nanopower Buck Converter As an example of high efficiency, the nanopower ultralow 330nA quiescent current buck (step-down) DC-to-DC converter shown in Figure 4 operates from a 1.8V to 5.5V input voltage and supports load currents of up to 175mA with peak efficiencies of 96%. While in sleep mode, it consumes only 5nA of shutdown current. The device is housed in a space-saving 1.42mm × 0.89mm, 6-ball wafer- level package (2 × 3 ball WLP, 0.4mm pitch). If higher currents are desired based on the power level in the NB-IoT or LTE-M networks, sister parts can deliver higher currents.
Figure 6. MAX38640 efficiency curve. Figure 4. An integrated buck converter.
Conclusion Asset trackers, depending on their specific application, must operate in the field for several weeks to a few years powered only by small batteries. This type of operation requires careful selection of each block for minimum power consumption. The buck regulator must operate efficiently over a wide input current range, from tens of microamps to hundreds of milliamps. The MAX3864x nanopower buck converter family, with its high efficiency and small size, provides an ideal power solution for asset tracking applications.
FEBRUARY 2024 | ELECTRONICS FOR ENGINEERS 45
Figure 5. Asset tracker buck converter application (7.1mm2 net area).
Small Size
The nanopower buck converter’s application footprint is shown in Figure 5. Thanks to its WLP package, high switching frequency operation, and small external passives, the net PCB area of the buck converter is a meagre 7.1mm2.
Efficiency Advantage Figure 6 shows the efficiency curve of the buck converter with a 3.6V input and a 1.8V output. Synchronous rectification at high load and pulsed operation at light load and ultralight load assure high efficiency across a wide operating range. An 87.5% high efficiency operation at 100µA
and 92% efficiency at 100mA make the IC ideal for asset tracking applications. This buck converter has the advantage of several efficiency points compared to alternative solutions.
The benefits of high efficiency and smaller footprint go hand in hand, resulting in less heat generation. This helps in designing a smaller, cooler asset tracker, easing concerns of the device overheating.
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