General Description
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 I
2
C interface
typically connected to a MCU inside the charger cradle to initiate the single wire con-
nection to the client device. Furthermore it enables readout of AS3447 register and I
2
C
sensors which are connected to the AS3442 I
2
C 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 I
2
C 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.
Bene ts
- Simultaneous battery charging (up to 150mA) and
communication to earpiece with only two pins
- Reduced number of mechanical connections
to accessory
- Enables smaller footprint with enhanced
communication capabilities
- Increased design exibility of accessory
- Enables data exchange between charger
cradle and accessory
Features
- Showing the battery level of the charging box
on the phone (instead of LED on the box itself )
- Automatically pair wireless earbuds with the phone
when opening the charging case
- Restoring acoustic parameters to earphone
in production line for ANC, beamforming
after calibration
- Enabling headphone makers to build smaller
and better-looking earbuds
- Accessory Firmware Updates
Block Diagram
Charger Cradle
Earphone
Charger
DCDC
Step Up
Power
Battery
Charger
Li-Ion Battery
POWER
IRQ
MCU
Power
I
2
C
IRQ
GPIO
Power
PWR
Power
Management
I
2
C
GROUND
I
2
C
Master
I
2
C
AS3442
I
2
C
IRQ
I
2
C
Master
I
2
C
Slave
GPIO
I
2
C
PMU
Sensor 5
Sensor 4
IRQ
PWR
AS3447
MCU
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© 01/2018 by ams
Subject to change without notice
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ams AG
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Phone +43 3136 500-0 · Fax +43 3136 525-01
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IRQ
I
2
C
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