True wireless headphones often use 3 (or more) pins to connect to their charging box for transmitting data and power. Additional pins require a larger space while also leading to risks of reliability. In addition, a fixed voltage is often used during the charging of the earphone battery, which causes harmful heating. In this design, we examine the shortcomings of these methods in detail, and then propose a mixing method that uses two ICs to solve these problems.
Overview
In Oriental culture, the big ears symbolizes good luck and wealth. Regrettably, most people in the world have not had a good luck and wealth - all the shapes and size of each person. True wireless headset (Figure 1) The manufacturer certainly cannot count on each user with a pair of big ears that can wear headphones. Instead, they need to overcome a huge challenge: the headphones can adapt to the various size and shapes Also let users feel comfortable.
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Figure 1 (a). True wireless headset. Figure 1 (b). True wireless headset and its charging box
Size constraint is not their only challenge. In essence, true wireless headphones must be repeated. However, if the charging efficiency is not high, the ear is rapidly fever, reaches high temperatures, thereby limiting its charging speed and making it uncomfortable. In this design, we discuss the management of wireless headset battery, and the challenges faced by the minimalized area of the small outer casing. We propose a way to save space with IC, which uses innovative ways to manage power and data transfer between headphones and their charging boxes. Finally, we will introduce a DC-DC converter IC that can adapt to optimizing battery charging conditions, thereby minimizing power wasteful in thermal form, helping to shorten the charging time.
Headphone charging interface
When the true wireless headset is placed in the charging box, the headphones start charging. Figure 2 shows a simplified block diagram of the configuration scheme.
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Figure 2. Simplified map of headphones and charging boxes
Headphone manufacturers often use 3 (or more) pin interface to manage battery charging processes. Two pins are used to charge, other pins provide communication (or data) channels between charging boxes and headphones. The channel is used to track the state of the battery in the charging box and the headset, meaning that the user and system can continue to obtain the status of the charging process. The communication interface can also be used for device firmware upgrade and / or factory debugging. Some headset models use a dedicated (POGO) pin to detect if the headset is placed in the charging box. Although some manufacturers use Hall effect sensors to avoid using dedicated POGO pins, this requires additional additional components in the charging box.
In order to accommodate additional pins inside the tiny headset, no matter what purpose, it has brought challenges to manufacturers, not limited to space, but also reliability, because each pin is introduced in the manufacturing process. Ideally, only two pins should be used to connect the headphones to the charging box. One way to achieve the above is to use two transmission pins and all road independent Bluetooth® channels to implement data communication between the charging box. However, this requires an additional Bluetooth transceiver in the charging box, which takes up even greater space and power consumption.
Combine data and power transfer together
For headphones and their charging box, a more efficient method is to combine data and power transfer to a single channel, effectively superimpose the data signal to the power source. This is called "power line communication" (similar to the power outlet is used to extend wired network communication). The MAX20340 implements innovation of this technology, providing a bidirectional DC power line communication interface for space-limited portable consumer electronic devices. With this method, the number of pins can be reduced to 2, which is a perfect solution. Figure 3 shows the MAX20340 DC power line communication management IC is integrated into the headset and its charging box, supports two-way data transmission with a rate of 166.7 kbps. The host IC is located in the charging box, each with addressable slave ICs in each headset.
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Figure 3. Data and power transmission between headphones and charging boxes utilizing the MAX20340
The interface only uses two pins to effectively reduce the number of fault points, thereby increasing reliability. The MAX20340 has other many advantages. The maximum charge current of the device is 1.2A, and the battery is charged faster. The device has an automatic slave detection function that means that the Hall effect sensor does not require a POGO pin, and the charging box can identify whether the headset is put in. Devices include high ESD protection without additional TVS diodes. The IC uses a 9 solder ball, a 0.4mm weldube, 1.358mm x 1.358mm wafer stage package (WLP).
Reduce fever
To prevent fever, the headset battery charging should be efficient as possible. By analyzing this process, it will be found to be unknown. The lithium ion battery (typically 3.7V) in the battery case is usually boosted to 5V using the DC-DC converter IC, and then the linear charger in the headset is used to charge the battery. However, even if the headphone battery is raised during charging, it always remains below 5V. This high voltage can cause power to waste in the form of heat. In order to prevent waste, during the charging process, the voltage difference between the input of the linear charger (provided by the boost converter) and the battery voltage should be changed as the battery voltage is increased, thereby minimizing.
The liter / buck converter shown in Fig. 4 can achieve this, the IC adopts a technique called dynamic voltage regulation (DVS)
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Figure 4. MAX20343 liter / antihypertensive DC-DC converter with DVS
Figure 5 shows how the MAX20343 is used in conjunction with the MAX20340 to reduce heat dissipation. The MAX20340 intermittently queries the headset battery voltage and supplies the information to the microcontroller on the charging box side. The microcontroller then adjusts the output voltage of the MAX20343 to match the additional margin required for the headset battery voltage plus linear charger. Such advantage is to minimize the energy waste of the charging box side battery and reduce heat dissipation in the headphones. The reduction in heat dissipation means that the headphones can charge at a faster rate. The MAX20343 can choose 16 solder balls, 1.77mm x 2.01mm, 0.4mm weld, WLP package, or 12-pin, 2.50mm x 2.50mm, 0.5mm weld distance FC2QFN package.
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Figure 5. Charging using the MAX20340 and MAX20343
Summarize
The true wireless headphones are slightly small, bringing many design challenges. We have seen that in addition to the power transmission medium, the true wireless system requires a way to achieve two-way data communication between headphones and charging boxes. Many models of headphones use additional pins to provide data channels, and also enable the charging cartridge to identify whether the headphones have been placed through a dedicated POGO pin. However, additional pins take up limited space to increase additional fault points. This can lead to reliability issues during the manufacturing process. We also discussed the form of energy during the charging process of headphones. We introduced two ICs that overcome these challenges. The MAX20340 combines power and data transfer to a channel, which means that only two pins can be connected to their charging boxes. The MAX20343 reduces fever by increasing the efficiency of the battery charging process. These ICs are ideal for similar applications, such as hearing aids, game handles, handheld radio walkie-talkies, sales terminals.
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This article author:
Josh fankhauser, Maxim Integrated Wearable Power Management Product Business Manager
Michael Jackson, Maxim Integrated Chief Author
This article is reproduced in the US letter semiconductor
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