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What engineers need to know about power management ICs

GreigRS
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The semiconductor industry continues to drive down the dimensions of the features used to fabricate integrated circuits. As a result of these smaller geometries, every new generation of ICs has a lower core voltage. This provides major benefits in terms of power dissipation, but it creates challenges with respect to managing that power. Digital devices running from sub-1V power supplies are more susceptible to noise, surges and droops on the supply rail, so managing the power becomes a critical part of system design.

Power has always been an important system function but now its management is integral to overall functionality. This article covers why power management is now so important, what kinds of power management devices are being developed, and takes a look at how power management can be used to develop more sustainable solutions.

Is power management really needed?

Power management covers a wide number of functions, from conversion to regulation, surge protection and brown-out recovery. A steady source of power is essential, particularly for very low power digital circuits and highly sensitive analogue functions. In modern IoT devices, endpoints or nodes, it is extremely common to combine low power digital processing combined with analogue frontends for sensors, both have specific and possibly varying power supply requirements, but with just one common power source.

Techniques such as buck/boost conversion, linear regulation and point-of-load power distribution now make up a significant amount of a total system. Every integrated circuit in a design could potentially have different power supply requirements. Putting all, or at least a significant amount of the power management into a single device can save board space and system power, as well as simplify the BoM.

The ability to integrate all or many power management functions into a single, low power device can be particularly beneficial in applications that are powered from batteries or even harvested energy. This is becoming increasingly viable as the power consumption of ICs continues to drop. When running from harvested energy, every last joule is important. Ultra-low-power PMICs can be used in these applications to get the most from renewable energy.

Five things to know about Power Management ICs

  • Why use a PMIC?

    PMICs, or power management ICs, are often used when a circuit needs to include multiple supply rails at different voltage levels, but all sourced from one single supply. A PMIC will integrate switching circuits with regulation and stabilisation, as well as short-circuit protection, along with over-voltage and over-current detection.

    Power sequencing is another important and valuable feature that PMICs can offer. In modern circuits it is sometimes necessary to control the way power is applied, by sequencing the rails. This essentially means turning on power rails in a predetermined way, such that the circuits powered from one supply are operating fully before the circuits powered from another rail start working. This can be necessary to protect interfaces or avoid outputs being driven high/low erroneously.

  • Do battery-powered IoT devices need PMICs?

    Even devices that run solely from primary cell batteries need voltage regulators. They are needed to stabilise the voltage when the battery is both new and when it is almost fully depleted. Using a PMIC to regulate the battery voltage can bring benefits. Often, the PMIC will draw a lower quiescent current than a linear regulator, but it may also include boost converters to get the most out of the battery cells.

  • Are PMICs needed for wireless sensor networks?

    In general, every kind of circuit can benefit from power management. Wireless sensor networks typically include multiple small, often battery-powered devices, that communicate in short bursts, typically in an event-driven way. This type of operation can take the form of short bursts of activity followed by relatively long periods of inactivity. This energy profile can put a strain on a battery but is just the kind of application that a PMIC was made for.

  • Are PMICs suitable for energy harvesting applications?

    Wireless sensor networks (WSNs) using a low power protocol such as Zigbee or Bluetooth LE are increasingly common. The various system functions can now be carried out using extremely small amounts of power, while the application profile often supports long periods of little or no activity. What’s more, WSNs are really useful in remote areas, but often access to power is limited and the cost of service visits for battery replacement prohibitive. This means that energy-harvesting is a good fit for remote, ultra-low-power WSNs.

    Capturing and storing renewable energy requires some form of power management and there are now several PMIC solutions on the market designed for just this kind of application. They have been designed to consume minimal power as well as interface and control various types of energy-harvesting technologies, such as solar cells or mini-turbines.

  • How do you choose the right PMIC?

    The right PMIC depends on the application. For battery-powered or energy-harvesting applications, the overriding requirement will be for low quiescent current, while in other applications it may be more important to provide flexibility in the output voltage levels available.

    Applications that communicate using wireless technology such as Bluetooth will also need to be able to sustain a reliable power rail for the duration of the transmit and receive periods. This makes power management imperative.

Technologies influencing power management

The supply voltage requirements for digital ICs continue to diverge; the voltage level is reducing while the power demand is increasing. Operating from 1V or below puts greater demand on the supply rail. The requirement is for a regulated and stable power supply that can react to bursts of activity. Wireless and RF communications are essential to wireless sensor networks or other wireless IoT endpoints. These types of devices are often battery-powered and are now even powered using harvested energy.

Power management in these types of applications takes on a new profile. It needs to provide reliable buck/boost operation with regulation and perhaps even power sequencing, in a device that takes up as little space and power as possible.

In the future, the level of integration will increase, and at some point that may even result in SoCs that combine a radio frontend with PMIC functionality. Today, the solutions available meet many of the engineering community’s needs, but those needs are likely to evolve quickly as more devices adopt wireless connectivity and more diverse power supply solutions.

Favourite things are Family, Music and Judo. Also, I have the ability to retain and quote useless facts, something that pleases me but can annoy others. My engineering hero - Isambard Kingdom Brunel

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