An analysis of low quiescent current in the most common small battery-powered devices

Do you know about miniaturized batteries? What are its challenges? Thanks to advances in miniaturization, Bluetooth® communications, and embedded processing, modern hearing aids have more features than ever before, from streaming music to being able to listen to music via your smartphone. App adjusts hearing amplification.

However, these enhanced capabilities come at a price: modern features require more power. The increase in power consumption is a challenge for engineers designing hearing aids, primarily because older versions used disposable zinc-air batteries. The battery life of these batteries is typically about two weeks. But when you add more features to your hearing aids, such as giving them the ability to play music, battery life can drop to hours. That's why engineers are using rechargeable lithium batteries in next-generation hearing aid designs.

Rechargeable lithium batteries add complexity to power systems in a number of ways, the most important being how to charge the batteries safely and accurately. There are additional design considerations when using two hearing aids. Because the left and right earphones are not physically connected, they cannot be charged simultaneously via a single cable. As a result, almost all new hearing aids now come with a box that has charging and storage capabilities.

The box is designed with specific jacks for each earphone to ensure proper charging. Charging of the earphones must be precise as rechargeable hearing aids are typically 25 mAh-75 mAh and the charging box ranges from 300 mAh -70 0mAh. This means that the earphones can be used for approximately 24 hours and approximately 10 charge cycles before the case needs to be recharged.

With the charging case, hearing aid designers can now consider three different lithium batteries: one for the charging case and two for the earphones. The choice of battery charger plays an important role in the design.

Also note that charging the battery from the battery (i.e. charging the headphone battery from the charging case battery) is not as simple as charging from the wall socket, as the voltage difference between the two batteries will not be very large. There must be internal circuitry to enhance the voltage difference between the charging case and earphones to achieve full charging. As the battery discharges, its voltage is slowly decreasing. Observing the discharge curve shown in Figure 3, when the battery capacity is about 50%, the charging box voltage is about 3.6 V. But this means that without boost, the charging case can only charge headphones up to 3.6 V, even though the energy stored in the case is enough to fully charge them.

In this case, most engineers would consider boosting cautiously. While discreet boosting does work, it often adds solution size and inefficiency by adding additional boost and inductor components to the power architecture.

To overcome these challenges, consider portable charging supported by quiescent current. For example, TI's BQ25619 battery charger and BQ25155 linear charger support charging without external boost. In hearing aid applications, you can place the BQ25619 in the charging case and the BQ25155 in each earphone.

Moreover, it is not always necessary to boost the charging box output to 5V. By using the boost function of BQ25619, it can be boosted to the minimum voltage required to leave sufficient headroom between the charging box and the headphone battery. This reduces unnecessary boost power loss and also increases headphone charging efficiency because the voltage difference is reduced.

The BQ25155 is ideal for headphones because its minimum 3.4V input voltage enables longer charging without boosting, and its 43µA quiescent current increases battery runtime. At the same time, the BQ25619's 7μA quiescent current in factory mode maximizes the life of the charging box. The BQ25619's 20mA charge termination current enables it to charge small batteries with a 7% increase in capacity.

The good news is that these advantages are not limited to hearing aids: all dual-battery device systems, including earbuds and wearable patches, can benefit from these innovations. TI will continue to use dual charger configurations in future designs, with the following features:

·Provides more efficient charging for the earphones and charging case while providing battery monitoring and protection and reducing the total bill of materials with integrated boost.

·Only one communication line is needed to reduce the number of pins in the headset and charging box. Using the BQ25619 and BQ25155, you can improve the number of charge cycles you can extract from the charging case without increasing cost or solution size. The above are some challenges of battery miniaturization. I hope they can help you.