3.4.2.1 USBA Host/Device
The USBA port can act as a USB device or USB host interface and can be accessed via the USB micro-B connector (J7).
Two resistors (R186 and R188) are placed on its power rail to form a voltage divider, converting 5V into 3.3V voltage that is then used to indicate the presence of a USB host to the MPU (USBA_VBUSDETECT_PD11).
In the case of board bring-up, USBA is the default port used to connect to the MPU over SAM-BA (SAM Boot Assistance). For more information, refer to the product web page.
The USBA port is also used as a secondary power source, as described in Power Supply Topology and Power Distribution. In most cases, this port is limited to 500 mA.
| Pin No. | Signal Name | Signal Description |
|---|---|---|
| 1 | USBA_VBUS_5V | First port 5V power |
| 2 | USBA_N | First port data minus |
| 3 | USBA_P | First port data plus |
| 4 | ID | – (not used) |
| 5 | GND | First port ground |
| PIO | Signal Name | Shared | Signal Description |
|---|---|---|---|
| PD11 | USBA_VBUSDETECT_PD11 | – | VBUS detection |
In Host mode, the USB host port A is equipped with 500-mA high-side power switches to enable self-powered and bus-powered applications. The USBA_EN_5V_PB2 signal controls the current limiting power switch MIC2025, which in turn supplies power to a client device. As per the USB specification, bus-powered USB 2.0 devices are limited to a maximum of 500 mA, therefore the MIC2025 limits the current and reports an overcurrent with the USBA_OVCUR_PC7 signal. For more information about the MIC2025, refer to the product web page.
| PIO | Signal Name | Shared | Signal Description |
|---|---|---|---|
| PB2 | USBA_EN_5V_PB2 | – | Power switch enable (active high) |
| PC7 | USBA_OVCUR_PC7 | – | Indicates overcurrent (open drain) |