The MCP2221A is a USB-to-UART/I2C serial converter. It bridges the gap between a computer's USB port and the UART interface on the MTCH9010 Evaluation Kit. A green LED labeled “ENUM” in the silkscreen indicates successful enumeration with the host computer. The MTCH9010 UART connection is shared between the USB bridge and the edge connector. A fixed 3.3V supplied by the onboard regulator (U204) powers the USB bridge for optimal USB performance.Figure 3-1. USB Bridge Overview
Tip: Drivers, CLI tools and apps are available to interface with the MCP2221A on its web page.
Power Considerations
Level shifters are used in the UART connection between the USB bridge and the MTCH9010 to accommodate the operating voltage range of the MTCH9010. These level shifters are powered by two separate supplies: VCC_BRIDGE, corresponding to the USB bridge, and VCC_SYSTEM, corresponding to the MTCH9010. If either power supply voltage drops to zero, the level shifters enter their tri-state mode, placing their outputs in a high-impedance state. This mode electrically isolates the RX and TX UART lines, preventing interference or backflow currents between the USB bridge and the MTCH9010.Figure 3-2. Level Shifters
Disabling USB Bridge
When SW200 is in the ‘OFF’ position, the MIC94163 (U205) power switch is disabled, pulling the
USB bridge RESET pin low and cutting power to the VDD and VUSB
power pins. With the RESET pin pulled low, the USB bridge
remains in reset, preventing unwanted transmissions on the UART or USB interfaces.
With the power switch disabled, the level shifters will also enter their tri-state
mode.Figure 3-3. USB Bridge Slide
Switch
