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.

Figure 3-33. USBA Port Schematic
Table 3-22. USBA J7 Connector Signal Descriptions
Pin No.Signal NameSignal Description
1USBA_VBUS_5VFirst port 5V power
2USBA_NFirst port data minus
3USBA_PFirst port data plus
4ID– (not used)
5GNDFirst port ground
Table 3-23. USBA PIO Signal Description
PIOSignal NameSharedSignal Description
PD11USBA_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.

Figure 3-34. USBA Port Power Switch Schematic
Table 3-24. USBA Power Switch PIO Signal Descriptions
PIOSignal NameSharedSignal Description
PB2USBA_EN_5V_PB2–Power switch enable (active high)
PC7USBA_OVCUR_PC7–Indicates overcurrent (open drain)