“Like other battery-operated, wirelessly-connected products in the IoT era, TWS faces severe power management challenges. Just like the need for “charging piles” to replenish energy and extend the range of electric vehicles, the charging bin of TWS has also become a key part of improving the battery life of the headset. Fortunately, innovative technologies are continuously improving the battery life experience of TWS, which will further promote the continuous development of the entire TWS market and create conditions for the birth of other Hearables products with new concepts.

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According to the latest data released by IDC, global shipments of wearable devices are expected to reach 396 million units in 2020, an increase of 14.5% compared to 2019. From the perspective of the wearable market segment, Hearables accounted for nearly 60% of the total shipments, and the performance was very eye-catching.

Figure 1: Global wearable market shipment analysis (Source: IDC)

One of the most important drivers behind the fact that hearable wearables can reach such a large scale is the rise of TWS true wireless earphones. Since Apple launched AirPods in 2016, it has achieved great market success in a short period of time – now on the daily commute to get off work, you can always see the white “tadpoles” passing by the ears of pedestrians , the market penetration rate of AirPods is evident.

This also triggered the entry and follow-up of other friends, and finally achieved the overall prosperity of the TWS market. According to IDC’s earlier market analysis, TWS headsets have maintained a 100% growth rate in the past few years, with shipments reaching 120 million units in 2019, and are expected to exceed 200 million units by the end of 2020.

Figure 2: Global TWS headset market trend and market share of each manufacturer (Source: IDC)

However, from the analysis data, we can clearly see that despite being besieged by “wolves”, Apple still occupies the top spot in the TWS market with a market share of more than 40%. This is related to its preconceived market strategy, but on the other hand, from the perspective of comprehensive product performance, TWS products that can compete with AirPods are indeed phoenix water chestnuts. Many manufacturers, including some brands that have made great achievements in the field of Bluetooth headsets in the past, have stepped on the pit of the first generation of TWS products. It can be seen that the technical threshold of TWS cannot be underestimated. With industry benchmarks like AirPods ahead, the pressure on latecomers is naturally not small.

From the point of view of the end user, the appetite of consumers is also getting higher and higher, and the requirements for TWS products are also increasing – the sound quality of TWS should not be too “boiled water”; Eat chicken”; in terms of noise reduction, whether it is passive or active, in short, make a difference… Of course, there is also the most critical indicator, that is, the battery life of TWS should be as long as possible, the longer the better!

To be honest, in a headset that weighs only a few grams, it is difficult to squeeze out the main control Bluetooth chip, audio decoder, speaker, microphone, memory, sensor and other components. The battery is even more difficult, which also makes TWS headsets generally inferior to traditional Bluetooth headsets in terms of battery life. However, for this, AirPods has given a reasonable solution, which is to use a headphone storage charging compartment to charge the headphones at any time when they are not in use. The cumulative battery life of the earphones has been greatly increased – the total battery life of the first-generation TWS is 10-20 hours through the charging bin, and the current latest TWS has increased to 25-30 hours.

Compared with earphones with small space and cramped space, people may think that the design of the TWS charging compartment will be much easier, but in fact the challenges are not simple. The most prominent challenges come from two aspects:

・ Smaller size: As a portable device, the size of the TWS’s charging compartment will also be constrained, and from the current trend, new functions will continue to be added to the charging compartment—such as wireless charging—so it can be used in space. Utilization also needs to be compared.
・ Higher efficiency: The efficiency is not high, which may cause the earphones to heat up during the charging process, thereby affecting the charging speed, and also causing more energy loss, affecting the total battery life.

To solve the above problems, it is necessary to provide assistance with specially optimized products. The good news is that we have been able to see targeted products and solutions in the market.

For example, in terms of simplifying the earphone charging circuit and compressing the system space, Maxim Integrated has proposed a novel solution before.

In the traditional TWS charging process, 3 or more pins need to be used, two of which are used for charging, and the other pins are used to establish a communication (or data) channel between the charging box and the headset. On the one hand, tracking The charging status of the headset battery is used to regulate the charging process, on the other hand to implement device firmware upgrades and/or for factory debugging, and in some solutions, a dedicated (pogo) pin is used to detect whether the headset is placed in the charging case. But more pins means increased circuit routing complexity and introduces additional reliability risks.

Figure 3: A typical charging case is a headphone charging circuit that requires at least 3 pins (Credit: Maxim)

In this regard, Maxim Integrated proposed a “power line communication” solution – the MAX20340 DC power line communication management IC, which combines data and power transmission into a single channel, superimposing the data signal on the power supply, so that only 2 The pin can realize power transmission (maximum charging current is 1.2A) and bidirectional communication (rate up to 166.7kbp) at the same time, and the whole charging system is simplified accordingly.

Figure 4: The MAX20340 requires only two pins for data and power transfer between the headset and charging case (Credit: Maxim)

Maxim Integrated has also come up with a unique solution to improve the efficiency of charging the earbuds from the charging case.

In a typical charging scheme, the lithium-ion battery in the charging compartment will charge the TWS earphone with a voltage of 5V. Even if the battery voltage of the earphone gradually increases with the charging process, the voltage output by the charging compartment is the input of the linear charger for the earphone. Voltage – will always remain at 5V, and such a high voltage will cause more power to be dissipated as heat, affecting overall efficiency.

Maxim Integraetd solves this problem in the new MAX20343 step-up/step-down converter by using dynamic voltage scaling (DVS) technology – during charging, the voltage output from the charging bin (the headphone linear The voltage difference between the input voltage of the charger) and the battery voltage changes as the battery voltage increases, thereby reducing energy loss and improving efficiency.

Figure 5: The MAX20343 buck-boost converter uses DVS technology to improve charging efficiency (Credit: Maxim)

The above-mentioned MAX20340 and MAX20343 are used together to form a TWS charging bin solution featuring miniaturization and high efficiency: MAX20340 queries the battery voltage of the headset intermittently, and provides this information to the microcontroller in the charging bin; The Controller adjusts the output voltage of the MAX20343 to match the headphone battery voltage plus the additional margin required by the linear charger. This minimizes the energy waste of the battery in the charging compartment and prevents the headphones from overheating during charging. for faster charging rates.

Figure 6: TWS charging bin solution implemented by MAX20340 and MAX20343 (Source: Maxim)

Like other battery-operated, wirelessly-connected products in the IoT era, TWS faces severe power management challenges. Just like the need for “charging piles” to replenish energy and extend the range of electric vehicles, the charging bin of TWS has also become a key part of improving the battery life of the headset. Fortunately, innovative technologies are continuously improving the battery life experience of TWS, which will further promote the continuous development of the entire TWS market and create conditions for the birth of other Hearables products with new concepts.