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8th July 2021

How to Design for Low Power

What is low power design?

Low power design is a series of techniques in power consumption reduction which prevent a device from using too much power.

What are the benefits of low power design?

Low power design means a longer battery life, which results in greater user experience for customers due to the extended periods between battery changes. Longer battery life of a product can also lead to lower maintenance costs, as costly visits to replace batteries occurs less frequently.

In addition, it’s better for the environment and there may be green funding incentives available for developing your product.

In essence what that means for you is better product reviews due to a more reliable product (less likely to run out of power whilst in use).

How to design for low power

This can be split into three main areas.

  1. Hardware
  2. Software
  3. Testing
  4. Design Hardware for low power

Quiescent power must be as low as possible:

  • Inactive or dormant sources of power should be reduced through careful engineering design.
  • Power supplies can even be a source of power usage themselves.
  • DC-DC converters need careful consideration as they need to be efficient over their expected load range, and have a low quiescent consumption themselves.

Components

One consideration for components and low power design is whether they can they be powered down or have low power sleep or idle modes? What current are consumed at those sleep or idle modes.

There are current chip shortages so you’ll also need to Design For Availability (DFA).

Related Article: Why are there chip shortages and what you can do about it

Low-power microcontrollers

Microcontrollers can have a big impact on power consumption so a lot of thought goes into reducing the power consumption of microcontrollers

  • Do your microcontrollers have low power sleep or idle modes?
  • Time and ease of entering/exiting sleep
  • Can peripherals still operate in sleep?

Once you have designed your hardware for low power you need to consider how your embedded software can influence power.

1. Configuring hardware for low-power:

Review and revise your functionality for the product. Are you sure you need that high power device or feature? Designing for low power is often a functionality trade-off which boils down to physics. If the functionality of the device is critical to its success, then it is important that everything that is not needed is shut-down (external devices, internal peripherals, GPIO pins).

Determine the lowest power sleep mode of the micro that can be used.

Generally, the greater the sleep mode, the less functionality available (including RAM retention).

2. Embedded Software for the best power consumption

Determine the system requirements:

The number 1 priority for long battery life is to do NOTHING for 99.9% of the devices operational lifetime!!! What does your device really need to do? Everything the device does has a cost in terms of battery life.

Essentially the mantra should be, when something needs to be done, do it as quickly as possible then go back to sleep.

General operation:

Here’s how it should look.

Initialise the system.

Ensure everything is configured to use as little power as possible.

Go to sleep.

Wait for an event that will either trigger a peripheral / set of peripherals to do something without processor interaction (preferred).

Or, wake the micro and do something.

If the micro has been woken, go back to sleep. Ensure all peripherals and external devices have been put back into low power modes.

Once you have configured the hardware and the software is functional, you should accurately measure the power consumption.

3. Testing for low power design

Use a power analyser. This accurately measures and logs the flow of power into your device. Do not rely on a  , no matter how accurate it is, it is easy to miss large but short-lived events that could have an impact on your power budget.

Analyse the power consumption over a reasonable length of time, ideally every type of event should be captured.

The next step is to determine the sources of power consumption. Hopefully this will be when the device is idle, as any reductions made here have a big impact on total power consumption. Don’t forget, this is the state the device spends most of its time in. Large spikes of power usage can seem daunting, but if they are short lived they may not be a problem (Energy = Power x Time).

Identify and remove/reduce any extraneous power consumption. Test again.

Finally you should be able to determine whether the battery will last long enough to cope with typical usage.

Related Service: Power Consumption Reduction

Using consulting for low power design

It is often best to work with an electronics design partner. They will work on low-power designs on a regular basis and have an in-depth understanding of the issues and challenges involved.

Need help with low power design?

The Ignys team specialise in power consumption reduction and can help you here. Talk about your project with us and get a feel for our team to see if we can help.

Start developing for low power design now

Authorship:

Peter Wortley is an experienced embedded software engineer at Ignys and has worked in both hardware and software engineering for over 20 years.

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