Discover the next generation of efficient, compact power management

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Discover the next generation of efficient, compact power management

Posted Date: 2024-01-30

Robin M. Saltnes, Nordic Semiconductor

Bluetooth Low Energy, Wi-Fi 6, and Cellular IoT bring connectivity to low-power IoT devices. Nordic SoCs, collaborative ICs and SiPs running these protocols are among the most power-efficient wireless solutions on the market, extending the battery life of IoT devices.

However, power management requires more than just efficient chips; power from the battery or power supply must also be regulated and distributed, and sometimes recharged if the device is powered by a rechargeable battery. This means that no matter how efficient the processor, radio and memory in a wireless chip are, if the power management system is not optimized enough, battery life will be affected.

Building compact power management systems in small packages

Building an efficient power management system is already a difficult task, while achieving a compact design is even more challenging. Space is limited in many IoT products, but traditional power management solutions often consist of multiple chips, such as voltage regulators, battery chargers, fuel gauges, external watchdogs and hard reset devices, which take up valuable space.

Nordic solves the efficiency and space challenges of power management with its nPM series of power management ICs (PMICs). The family includes the nPM6001 (with six independently controlled power rails), the nPM1100 (dual-mode configurable buck regulator and integrated battery charger) and the newly launched nPM1300. Optimized for maximum efficiency and compact size, this PMIC simplifies system design by integrating the essential functions required for reliable operation into a small package.

Intelligent power management provided by nPM1300

nPM1300 is available in a small 5 x 5 mm (QFN32) or 3.1 x 2.4 mm (WLCSP) package and integrates two buck converters, two load switches, a battery charger, USB-C compatible input, shipping mode and power count. This simplifies power management from up to eight chips plus related passive components to one chip plus several passive components.

In addition to its high level of integration, this PMIC provides critical system management functions that typically must be added separately to traditional power management circuits. These features include key items such as fail-boot recovery, hard reset, power-saving "sleep" mode, watchdog timer and power-down warning.

Accurate power measurement without power consumption

It is very useful for consumers to know exactly the remaining battery life of their IoT devices. Engineers typically do this by measuring the battery voltage, which represents the remaining charge, or for more precise results using a coulomb counter, a device that continuously measures the current flowing into or out of the battery to determine the battery's total charge.

The battery voltage measurement method is simple and easy to use and consumes little power, but its accuracy is not high, especially when the battery is affected by temperature changes. Coulomb counters are more accurate, but require additional components and consume more power. In contrast, the nPM1300 has a high-precision fuel gauge that combines the simplicity and lower power consumption of a battery voltage measurement with the accuracy of a coulomb counter.

Nordic experimentally compared coulomb counters, battery voltage measurements, and the nPM1300 fuel gauge. The peak error in battery voltage calculation is close to 20% compared to a coulomb counter. In comparison, the nPM1300's fuel gauge has a maximum error of only 2% compared to a coulomb counter, and most errors are within 1%.

Software driven fuel gauge

Key to the Nordic fuel gauge's ability to maintain high accuracy over a wide temperature range is a software algorithm driven by the main processor. Information used by the processor includes current flowing from the battery, battery terminal voltage, system voltage and battery temperature thermistor reading.

In order for the algorithm to generate accurate results, it must first "learn" the battery characteristics (this only needs to be learned once if the end product continues to use the same battery). Teaching is conducted using Nordic's Evaluation Kit (EK), which is equipped with a fuel gauge board providing suitable resistive loads and the Nordic nPM PowerUP application.

After calibration, with current, voltage and temperature inputs, the main processor uses an algorithm developed by Nordic to accurately derive the battery's state of charge over the life of the device. The power consumption at one second measurement frequency adds approximately 4 microamps to the typical overhead of the host processor.

Power management from battery to antenna

To maximize battery life, it is important to study how each part of a wireless product system affects overall power consumption. Developers need to optimize every component, from the battery all the way to cloud connectivity, including radio operation, processing and power management, to get the most out of power.

Designing based on Nordic SoC or SiP, one of the lowest power wireless chips on the market, and Nordic nPM6001, nPM1100 or nPM1300, users can get an excellent foundation to reduce the energy consumption of wireless products as much as possible.

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