3.4.3 USB Host/Device Interface

The USB (Universal Serial Bus) is a hot-pluggable general-purpose high-speed I/O standard for computer peripherals. The standard defines connector types, cabling, and communication protocols for interconnecting a wide variety of electronic devices. The USB 2.0 Specification defines data transfer rates as high as 480 Mbps (also known as High-Speed USB). A USB host bus connector uses four pins: a power supply pin (5V), a differential pair (D+ and D- pins) and a ground pin.

The board features three USB communication ports named USB-A, USB-B and USB-C.

On this board, the USB-A port can act only as a USB device interface and can be accessed via the USB Type-C connector (J3).

Two resistors are placed on its power rail to form a voltage divider, converting 5V into 3.3V that is then used to signal the presence of a USB host to the MPU.

The USB-A port is used as a power source, as mentioned in USB Supply Input. In most cases, this port is limited to 500 mA.

The USB-B port is exposed on a USB Type-A connector and acts as host.

The USB-C port is exposed on another USB Type-A connector and acts as host.

In Host mode, the USB host ports B and C are both equipped with a 500-mA high-side power switch output from one MIC2026 device to enable self-powered and bus-powered applications. USBB_EN_5V_PC20 and USBC_EN_5V_PC21 signals control the current limiting power switch MIC2026, which in turn supplies power to a client device. Per the USB specification, bus-powered USB 2.0 devices are limited to a maximum of 500 mA, therefore the MIC2026 limits the current and indicates an overcurrent with the USBB_OVCUR_PC18 and USBC_OVCUR_PC19 signals. For more information about the MIC2026, refer to the product web page.