Deliver Accurate Battery SOC Data from Your Wireless Android Headphones

September 18, 2019

Bakul Damle  By: Bakul Damle
 Director, Maxim Integrated 
Sagar Khare  and Sagar Khare
 Executive Business Manager; Battery Management, Maxim Integrated  


Settling into your seat for a five-hour flight, you pop in your Bluetooth earbuds to listen to some podcasts. Will the device’s batteries and charging case have enough juice to deliver lasting run-time? Before long, the answer to this question will be much clearer. That’s because Android has announced plans to make it easier to manage battery life on wireless Android headphones.

By the end of the year, Android users with Google Fast Pair Bluetooth devices will gain an array of new features natively via the operating system, including much more detailed battery life information. Those with True Wireless Stereo (TWS) headphones will be able to see battery life percentages for each earbud and also for the case. And they’ll be able to get notifications when their devices have reached certain percentages.

Considering these enhancements, it makes good sense to incorporate fuel-gauge ICs into your next wireless Android headphone design. This could make a notable difference in delighting your customers with precise and accurate battery state-of-charge (SOC) data.

Wireless earbudsFigure 1. By year end, Android users of True Wireless Stereo (TWS) headphones will have access to detailed battery life percentages for each earbud and the case.

Battery Life Data Will No Longer Be Invisible

TWS technology allows users to pair two audio devices via Bluetooth; the left and right channels can be transmitted separately. Google’s proprietary Fast Pair standard provides quick and easy discovery and pairing of Bluetooth devices on supported Android devices. TWS headsets have traditionally provided only very basic battery information—in other words, not quite enough detail for the user to determine whether the devices would require charging soon. The Fast Pair enhancements mean that users will receive, on their Android phones, granular battery life percentage information from each earbud and the charging case. They’ll even receive a pop-up notification with this data when they open or close the case. This means that designers who were once able to get by with simple color or bar indicators for battery life will now need to up their game and show much more precise information, or risk disappointing their customers. In addition, Bluetooth headset manufacturers who have been using fuel gauges will no longer need to develop a dedicated app for users to view battery information.

As a result of these enhancements, simple voltage measurements that provide rough estimates of battery SOC will no longer be adequate. Fuel-gauge ICs, which monitor batteries to provide an estimate of the remaining charge as well as data on the state-of-health, are a better option. But not all fuel-gauging technology is created the same. For optimal results, designs of wireless Android earbuds and headphones as well as their accompanying charging cases require fuel-gauge ICs that:

  • Deliver high accuracy, even in challenging operating environments
  • Have low quiescent current. Since the tiny batteries in these headsets typically support capacities no greater than 100mAhr, low quiescent current minimizes current draw while the devices are being used and reduces battery discharge when the devices are on standby
  • Are small, and do not require many extra discrete components, given the tiny form factors of these devices

Compact, Accurate Fuel-Gauge ICs Extend Battery Life

Maxim, which has a long history of developing accurate fuel-gauge technology for portable devices, can help wireless Android headphone designers meet the customer expectations that the Fast Pair enhancements will bring. Fuel-gauge ICs with our ModelGauge™ m5 EZ algorithm provide industry-leading battery SOC accuracy without requiring battery characterization. In simulations with more than 300 different batteries and 3,000 discharges, our results have less than 3% error in more than 97% of the most common test cases. In addition, with characterization, these fuel gauges have demonstrated less than 1% error. The devices also have low quiescent current, are available in small packages, and minimize the need for discrete components with their high level of integration. Used successfully in more than one billion devices, our ICs provide time-to-empty, time-to-full, and battery age data.

Some devices to consider for your next wireless headset design include:

  • MAX17048 1-cell/2-cell fuel gauge with the ModelGauge algorithm. This device provides low quiescent current (3µA hibernate, 23µA active) and eliminates the current-sense resistor and battery-learn cycles typically required in traditional fuel gauges. It is available in a 0.9mm x 1.7mm, 8-bump WLP.
  • MAX17055 1-cell fuel gauge with ModelGauge m5 EZ. This device has 7µA operating current; provides precision measurements of current, voltage, and temperature; and is available in a 1.4mm x 1.5mm, 9-pin WLP.
  • MAX17260 1-cell fuel gauge with ModelGauge m5 EZ and optional high-side current sensing. This device has just 5.1µA operating current and is available in a 1.5mm x 1.5mm, 9-pin WLP.

The following block diagrams show how fuel-gauge as well as power management ICs can support example TWS headphone applications.

TWS earbud and cradle with USB and wireless chargingFigure 2. TWS earbud and cradle with USB and wireless charging.

Block diagram of a TWS earbud and cradle with USB chargingFigure 3. Block diagram of a TWS earbud and cradle with USB charging.

When the Fast Pair enhancements on battery life become available, it will be an opportunity for TWS headphone designers to further enhance the user experience. Implementing fuel-gauge technology with high accuracy, low quiescent current, and small sizes into your designs can help you hit your targets.