What is TWS True wireless Stereo Bluetooth earbuds? - OEM factory

oem tws bluetooth earbuds factory deeply analyze what is tws Bluetooth earbuds.

TWS (True Wireless Stereo) Bluetooth earbuds is an extremely popular audio product in recent years. It uses the Bluetooth chip to first establish a wireless connection between the mobile phone and the main earphone, and then establish the wireless communication between the main earphone and the auxiliary earphone, thus completely abandoning the wire connection between the traditional earphones, which greatly facilitates the user's use. In addition, the main earphone can be used alone, which is fully capable of meeting the application requirements of a single Bluetooth earphone in the existing market, and the use function is very powerful. Therefore, since Apple released the first TWS earbuds-Airpods in September 2016, the market response has been very enthusiastic. Follow-up audio manufacturers quickly followed up and deployed TWS Bluetooth earbuds, making the TWS earbuds market colorful. Next, Bluetooth 5 will bring a more exciting user experience, and the new charging box design will make it more convenient for consumers.

Lightweight and easy to carry is the most important design goal of TWS earbuds. Limited by the small space of the charging box and earbuds, the battery capacity used in these two parts cannot be increased. The capacity of the charging box is generally within 1000mAh (in which 200- The most common in the 700mAh range), and the capacity of the earphone is smaller, most of which are less than 100mAh. Therefore, whether it is a charging box or a earbuds, attention should be paid to the low-power design of the system to ensure that the product has a longer use time.

1. Introduction to the charging box system

The detailed system block diagram of the charging box is as follows:

Figure 1 Block diagram of TWS charging box system

In the signal chain part, the sensor mainly has a Hall sensor to realize the opening and closing detection of the box. The LED light achieves a cool display effect, and the Bluetooth chip can transmit the box information to the mobile phone, which is convenient for the mobile phone to view the box power information. Button detection may require some logic devices, such as D flip-flops such as SN74LVC1G74, which can convert the pulse edge of the button into a level flip, which is convenient for the MCU to record the button information.

In the power rail part, the general input port is made of a 5V micro USB port (Apple’s Airpods are lightning ports, which are also 5V). Considering that there are many adapters that support high-voltage fast charging, the charging box needs an over-voltage protection chip for protection against misplugging, and a charger is added to charge the lithium battery. At present, many chargers integrate the function of overvoltage protection, but most of the overvoltage response time is us level. It is recommended to add an additional overvoltage protection chip for fast protection. For Charger, it is recommended to use a charger with power-path (path management). On the one hand, when the battery of the box is low, plug in the adapter to get a higher system voltage immediately, ensuring that the box can immediately power low-power headphones; On the other hand, when the fast charging current is set to be small, if the load needs constant load (such as driving LED lights), this part of the load is likely to be near the charger's cut-off current, and the charger may not be able to do it without the power-path function. If the battery is fully charged, the experience will be worse.

The battery is generally a single-cell lithium battery, which is generally provided by the battery pack manufacturer, and the fuel gauge and the secondary protection IC have been packaged to ensure more reliable operation of the battery. The power supply of a single lithium battery mainly supplies two parts: one part is boosted to 5V to power the earphones, and the other part is stepped down to 3V and below to the MCU/Sensor in the box.

TI's products are very rich, which can cover most of the needs of charging boxes. Here are a few ICs that are briefly recommended for use in charging boxes. The recommended indicators are mainly packaging and power consumption. Power consumption is mainly the quiescent current of the IC under enable. What needs to be mentioned is that since the overvoltage protection and the charger only work when charging, the adapter is plugged in and the power supply is sufficient, so these two parts do not require a small Iq, but should pay attention to the leakage current of the charger.

2. Introduction to the earbuds system

In the signal chain part, the Bluetooth chip is responsible for receiving the data sent by the mobile phone, and then pushing the headset through the amp. The sensor is mainly a gravity sensor, which detects signals such as headphone shaking. At present, the integration level of Bluetooth chip is very high, and it can also do some tuning functions.

The power rail part is limited by the very small headphone space, and the headphone end can no longer be used as the power supply port of the micro USB interface, and it is usually changed to a specific metal contact piece method. The earphone input power comes from the 5V after the charging box has been boosted and stabilized. Therefore, there is no risk of overvoltage in the earphone input, and it is not necessary to add overvoltage protection. A single lithium battery can be charged directly after passing through the charger. Similarly, the battery is also provided by the battery pack manufacturer, with integrated fuel gauge and secondary protection. The battery provides 2.5V or 1.8V power to the system through the LDO.

Compared with the design of the charging box, the space on the earphone end is smaller, which puts more stringent requirements on the packaging and power consumption of the chip. In response to this situation, TI’s plans on the headphone end are summarized as follows:

3. TI reference design

TI has a reference design TIDA-050007 for TWS headsets. The following figure is a system block diagram of the reference design. The power consumption of this reference design is only 18uA, and a simple algorithm is used to achieve dynamic adjustment of the boost. When the charging box battery voltage is higher than the earbuds battery voltage, the boost chip TPS61099 can also enter the pass-through mode to further improve the charging efficiency.