SLUAA04A june 2020 – may 2023 BQ25150 , BQ25155 , BQ25618 , BQ25619 , TS5A12301E , TS5A3157 , TS5A3159A , TS5A6542
True Wireless Stereo (TWS) customers strive to increase the number of earbud charges per full case battery and minimize heating during charging for a good user experience. It is most common to use a linear battery charger to charge the earbud batteries. Therefore, to maximize charging efficiency the case output voltage must be updated dynamically based on the current earbud battery voltage. This warrants the need for a communication interface between the case and the battery. In addition to earbud battery voltage, this interface can also communicate useful information such as charging status, device temperature, and other faults back to the charging case.
The number of pins required for the earbud-to-case interface is a key mechanical consideration in the design of TWS. Many implementations of earbud-to-case communication result in the need for three to five pins on each earbud. The minimum for charging, two pins, is ideal from a mechanical standpoint. The challenge then becomes how to implement a 2-pin communication interface while still allowing for charging to occur.