Bluetooth earphones are gaining popularity and mobile charging for these devices is mandatory. Both, earphones and charger cradle, are equipped with electronics and sensors, but the connection between the charging case and the earphones is typically limited to two wires – ground and power. Without enhancing the capabilities of the two wires only power transfer for charging the battery is possible.
The AS3442/47 allows to extend the functionality of the two wire connection to enable charging and simultaneous communication to the earpiece. The MCU inside the charger cradle can request data from the earphone while the charging process is on-going and vice versa. In order to operate the system two chips per side are necessary. The master device (AS3442), which is typically located in the charger cradle, and a client device (AS3447), which is located in the accessory. The master device features an I2C interface typically connected to a MCU inside the charger cradle to initiate the single wire connection to the client device. Furthermore it enables readout of AS3442 register and I2C sensors which are connected to the AS3442 I2C master interface. An interrupt signal line is available to detect status changes on GPIOs or if communication is interrupted. The client device features besides the I2C master interface up to 5 GPIOs which can be controlled via the host MCU. An interrupt input pin is available whose status signal is also transferred to host MCU accordingly.