In recent years, TWS (True Wireless Stereo) has been rapidly rising in the headset market. Now, users no longer need to worry about the entanglement of the headset cable when using streaming media devices. True wireless headphones are Bluetooth®-based wireless headphones. The left and right channels are separated into two individuals that are independent and paired with each other. Although this innovative design eliminates the need for users to connect their phones or other devices with wires, it poses a new set of design challenges for headset manufacturers.
In order to maximize battery life and battery run time, the headset must be properly positioned in the charging case and can be charged efficiently. A cost-effective method is to use a current detection amplifier to monitor the charging of the ear buds, and use the Hall-effect switch for the opening and closing of the wireless charging box and the position of the ear buds to maximize the battery charging efficiency and battery life.
Designing with a current sense amplifier
The battery capacity of TWS is usually below 100-mAh. Therefore, in order to protect and accurately charge these small-capacity batteries, we need more accurate current measurements. Traditional battery chargers and fuel gauges excel at monitoring the current of larger batteries, except the current at lower levels.
Dedicated current sense amplifiers are more accurate when measuring small currents. If you already have a microcontroller (MCU) or power management integrated circuit (PMIC) in your design, you can use the output of these amplifiers to monitor and measure battery usage and battery life based on algorithms written to the MCU or PMIC.
Placing two small current detection amplifiers (such as INA216) in the wireless earphone charging box can achieve high-precision charging current measurement. Alternatively, if solution size is a priority, a single dual-channel current-sense amplifier like the INA2180 is recommended.
If accuracy is not an important factor, and assuming equal current distribution, then a current sensor can monitor the charging of both earbuds. A bidirectional current-sense amplifier, such as the INA191 or INA210, is placed in the earbuds to enable both charging and measurement functions. No matter which topology you use, these devices will better protect the battery, because even small current changes will affect the battery life.
Designing with Hall-Effect Sensors
The new feature of TWS is innovation of charging and carrying out. The opening and closing of the charging box can be used to open or close the Bluetooth connection, and the in-box / out-box detection can determine whether to stop charging and pair the left and right ears. Other sensor technologies may not cost-effectively implement these functions with the right sensitivity, so choosing the right sensor is critical.
The Hall-effect sensor can be well applied to detect the charging of the earbuds. Since magnets have been used to close the charging case lid, using a magnetic sensing solution in the form of a Hall-effect switch to detect the lid is clearly a solution to connect / disconnect Bluetooth without additional parts. In addition, putting the magnet in the earbud is a method for effectively charging by detecting whether there is an earbud in the charging case.
Choosing the right digital Hall-effect sensor is very important, and the low frequency / low power consumption makes the DRV5032 the best choice. For the application of Hall-effect sensors in earplugs, it is possible to provide magnet detection information 5 times per second. This frequency allows you to use the DRV5032’s low-power option, which consumes only about 0.5μA of quiescent current without severely impacting battery life.
The state of charge and charging case detection are important for using a small-capacity battery and wirelessly connected earbuds. Current-sense amplifiers and Hall-effect sensors provide a solution for those struggling to design around these new features and challenges.
Read more sensor technology: http://www.apogeeweb.net/categroy/4.html