BC1.2 Devices (Experimental)
The Battery Charging specification, currently at revision 1.2, is commonly referred to as just BC1.2. BC1.2 defines limits and detection mechanisms for USB devices to draw current exceeding the USB 2.0 specification limit of 0.5A, 2.5W.
The BC1.2 specification uses the term Charging Port for the device that supplies VBUS on the USB connection and the term Portable Device for the device that sinks current from the USB connection.
Note that the BC1.2 Specification uses the acronym PD for Portable Device. This should not be confused with the USB-C Power Delivery, which also uses the acronym PD.
On many devices, BC1.2 is the fallback mechanism to determine the connected charger capability on USB type C ports when the attached type-C partner does not support Power Delivery.
Key parameters from the BC1.2 Specification include:
Parameter |
Symbol |
Range |
|---|---|---|
Allowed PD (portable device) Current Draw from Charging Port |
IDEV_CHG |
1.5 A |
Charging Downstream Port Rated Current |
ICDP |
1.5 - 5.0 A |
Maximum Configured Current when connected to a SDP |
ICFG_MAX |
500 mA |
Dedicated Charging Port Rated Current |
IDCP |
1.5 - 5.0 A |
Suspend current |
ISUSP |
2.5 mA |
Unit load current |
IUNIT |
100 mA |
While the ICDP and IDCP rated currents go up to 5.0 A, the BC1.2 current is limited by the IDEV_CHG parameter. So the BC1.2 support is capped at 1.5 A in the Zephyr implementation when using portable-device mode.
Basic Operation
The BC1.2 device driver provides only two APIs, bc12_set_role() and
bc12_set_result_cb().
The application calls bc12_set_role() to transition the BC1.2 device to
either a disconnected, portable-device, or charging port mode.
For the disconnected state, the BC1.2 driver powers down the detection chip. The power down operation is vendor specific.
The application calls bc12_set_role() with the type set to
BC12_PORTABLE_DEVICE when both the following conditions are true:
The application configured the port as an upstream facing port, i.e. a USB device port.
The application detects VBUS on the USB connection.
For portable-device mode, the BC1.2 driver powers up the detection chip and
starts charger detection. At completion of the charger detection, the BC1.2
driver notifies the callback registered with bc12_set_result_cb(). By
default, the BC1.2 driver clamps the current to 1.5A to comply with the BC1.2
specification.
To comply with the USB 2.0 specification, when the driver detects a SDP (Standard Downstream Port) charging partner or if BC1.2 detection fails, the driver reports the available current as ISUSP (2.5 mA). The application may increase the current draw to IUNIT (100 mA) when the connected USB host resumes the USB bus and may increase the current draw to ICFG_MAX (500 mA) when the USB host configures the USB device.
Charging port mode is used by the application when the USB port is configured as
a downstream facing port, i.e. a USB host port. For charging port mode, the
BC1.2 driver powers up the detection chip and configures the charger type
specified by a devicetree property. If the driver supports detection of plug and
unplug events, the BC1.2 driver notifies the callback registered with
bc12_set_result_cb() to indicate the current connection state of the
portable device partner.
Configuration Options
Related configuration options: