General
Review and verify the following for the custom schematic design:
- Above section including relevant application notes and FAQ links.
- Pin connectivity requirements, pin attributes and signal description.
- Referenced specific standard for electrical characteristics, timing parameters and any additional available information.
- Required USB interface configuration (Host or Device) and recommended connections.
- USB VBUS design guidelines based on the USB interface configuration. USBn_VBUS connection is optional for Host configuration. Connecting 5V supply from the USB connector directly to the USBn_VBUS pin is not recommended or allowed. Changing the data sheet VBUS recommended divider value is not recommended or allowed. VBUS fail-safe capability of the IO is valid only when the recommended divider values are implemented.
- Connection of recommended IO calibration resistor.
- Connection of the recommended USB supplies including filtering.
- Direct connection of the USB signals.
- Common-mode chokes can be used for EMI control. Adding common-mode choke can reduce the signal amplitude and degrade performance. Add provision to bypass the CMC using 0Ω resistors.
- Marking of differential signals and the differential impedance value.
- Implementation of USB power switch when USB interface is configured as HOST.
- USB power switch enable control using DRVVBUS (internal pulldown is enabled during reset).
- Connection of the power switch OC output to processor IO.
- Connection of the USB signals to the USB connector.
- Provision for recommended capacitors on the USB VBUS pin of the USB connector.
- Provision for required external ESD protections for the USB interface.
- In case USB boot is implemented, verify the errata, supported interface configuration, USB port and the connections.
Schematic Review
Follow the below list for the custom schematic design:
- USB interface connection matches the required USB interface configuration (Host or Device). Compare the interface connection with the EVM.
- External ESD protection and CMC implementation with provision to bypass using 0Ω resistors.
- VBUS voltage divider values (follow data sheet) and tolerance (1%). Follow the data sheet recommendations. Use of multiple resistors is allowed provided the value, tolerance and ratio is maintained.
- VBUS capacitor values used versus requirements (refer EVM).
- Power switch enable connection (in case processor USBn_DRVVBUS is used, pullup is not recommended or allowed since the DRVVBUS has an internal pulldown enabled).
- Connection of power switch OC output to the processor IO and IO level compatibility.
- Supply rails connected follow the ROC.
Additional
- In case a Type-C USB interface is implemented using TI devices, obtain a review of the implementation done with the relevant business unit or product line.
- A filtered supply (ferrite and capacitors) is used for VDDA_CORE_USB and VDDA_1P8_USB. VDDA_3P3_USB can be connected to the 3V3 SYS voltage. Refer specific and latest EVM for implementation as filters are being continuously optimized.
- Verify fail-safe operation of USB interface. Applying an external interface signal before supply ramps can cause voltage feed and can affect the custom board functions.
- When a CMC is used on the USB data lines, verify the connections including the polarity. Reversing the polarity can short the data signals.
- DNI USBn_DRVVBUS pullup and pulldown to implement wakeup from deep sleep.