By Anil Telikepalli, managing director of the Core Products business unit; Nazzareno (Reno) Rossetti, analog and power management expert; and Simo Radovic, principal applications engineer for Power Core Products
Maxim Integrated
www.maximintegrated.com
New, low-power data connections are sparking a proliferation of asset-tracking solutions thanks to their low cost of deployment. The effects can be seen in multiple applications, particularly transportation and supply chain management.
In a typical application, a sensor provides updates from a given location, transmitting data about temperature, humidity, pressure, and motion. The sensor needs to transmit only small amounts of data, which results in higher coverage and ultra-low power consumption, enabling far greater device longevity. The sensor’s battery must last from several weeks to a few years. Asset tracking, depending on the application, may require the deployment of several tracker devices. Accordingly, these asset-tracker devices must also be small, portable, and cost-effective.
In this design solution, we discuss the power management challenges encountered by a typical battery-operated asset tracker device and show an example using a small, high-efficiency buck converter.
Edge-to-enterprise communication
Fig. 1 illustrates a typical tracking communication chain. The asset being tracked transmits the data via a beacon, which reaches a server through a dedicated cellular network. From here, the data reaches the enterprise portal for asset management and analytics.
Fig. 1: Real-time GPS tracking.
In the factory environment, asset tracking brings the management of facilities, vehicle fleet equipment, and maintenance into a single platform, resulting in improved safety, productivity, and extended asset life.
Asset-tracking networks
A new generation of beacons connects directly to dedicated cellular networks (LTE-M, NB-IoT), eliminating the use of Bluetooth to communicate with a gateway. These technologies can be very different but are all characterized by low power consumption, enabling several years of battery life (Table 1 ).
Table 1: Networks characteristics.
Typical asset-tracker system
Fig. 2 shows a typical asset-tracker block diagram. The three-series alkaline battery supplies a charge of 2,000 mAh. A step-down regulator powers the on-board controller, sensors, and radio.
Fig. 2: Asset-tracker block diagram.
For demanding asset-tracking applications, the system must last for a year on three alkaline batteries, drawing only 100 µA in deep sleep and transmitting 100 mA once per day for about two minutes (Fig. 3 ). While it is true that, depending on power level and other options supported in the LTE-M or NB-IoT asset trackers, currents can be higher, for our discussion, we will stick to the 100-µA to 100-mA range.
Fig. 3: Asset-tracker current profile.
High-use performance requires careful selection of each block for minimum power consumption. The buck regulator must be efficient over a wide range from 100 µA to 100 mA. For instance, a 4% average loss of efficiency by the buck converter translates into a field deployment reduction of about two weeks.
Ultra-low quiescent current
The buck converter’s quiescent current is especially important because the device is in deep-sleep or quiet mode most of the time, consuming only 100 µA or less. With VOUT = 1.8 V, the output power during deep sleep is POUT = 1.8 V × 100 µA = 180 µW. With η = 90%, the input power is: PIN = 180 µW/0.9 = 200 µW
If the buck converter is not carefully chosen and has a typical quiescent current of 3 µA and a 3.6-V input voltage, there is an additional power dissipation of: P’IN = 3 µA × 3.6 V = 10.8 µW
The final buck converter efficiency is: η = POUT /(PIN + P’IN ) = 180/(200 + 10.8) = 86%
A quiescent current of 3 µA robs the buck converter of four efficiency points, draining the battery significantly faster!
On the other hand, a buck converter with 300-nA quiescent current will barely reduce the efficiency, lowering it only half a percentage point. For asset-tracking applications, it is critical to select a buck converter with ultra-low 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 ultra-low 330-nA quiescent-current buck (step-down) DC/DC converter shown in Fig. 4 operates from 1.8-V to 5.5-V input voltage and supports load currents of up to 175 mA with peak efficiencies of 96%. While in sleep mode, it consumes only 5 nA of shutdown current. The device is housed in a space-saving 1.42 × 0.89-mm six-pin wafer-level package (WLP 2 × 3 bumps, 0.4-mm pitch). If higher currents are desired based on power level in NB-IoT or LTE-M networks, sister parts can deliver higher currents.
Fig. 4: Integrated buck converter.
Small size
The nanoPower buck converter’s application footprint is shown in Fig. 5 . Thanks to its WLP package, high switching frequency operation, and small external passives, the net PCB area of the buck converter is a meager 7.1 mm2 . A 2 × 2-mm DFN package is also available.
Fig. 5: Asset-tracker buck converter application (7.1 mm2 net area).
Efficiency advantage
Fig. 6 shows the efficiency curve of the buck converter with a 3.6-V input and a 1.8-V output. Synchronous rectification at high load and pulsed operation at light and ultra-light load assure high efficiency across a wide operating range. An 87.5% high-efficiency operation at 100 µA and 92% efficiency at 100 mA makes the IC ideal for asset-tracking applications. This buck converter has an advantage of several efficiency points compared to alternative solutions.
Fig. 6: MAX38640A efficiency curve.
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 device overheating.
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 µA to hundreds of mA. The nanoPower buck converter family, with its high efficiency and small size, provides an ideal power solution for asset-tracking applications.
About the authors
Anil Telikepalli is the managing director of the Core Products business unit at Maxim Integrated with responsibility for Power and Data Converter products. Anil joined Maxim in 2010 and manages definition, product development, marketing, and business development with a global team across North America, Europe, and Asia. Prior to Maxim, Anil held multiple roles at Xilinx and MIPS Technologies in engineering applications, marketing, and business operations, enabling growth in communications, computing, consumer, automotive, and industrial markets. Anil holds master’s and bachelor’s degrees in electrical engineering from the University of Kentucky and Osmania University, respectively. He holds several patents in the field and has advised multiple hardware and internet software startups.
Nazzareno (Reno) Rossetti is an analog and power management expert at Maxim Integrated. He is a published author who holds several patents in the field. Reno has a doctorate in electrical engineering from Politecnico di Torino, Italy.
Simo Radovic is a principal applications engineer for Power Core Products at Maxim Integrated. He has more than 12 years of DC/DC switching converter experience. Simo holds a master’s degree in electrical engineering from San Jose State University.
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