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 allowed or recommended. Changing the data sheet
VBUS recommended divider value is not allowed or recommended. 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 / EMC
control. Adding common-mode choke may reduce the
signal amplitude and degrade performance. Add
provision to bypass the CMC using 0Ω resistors
- Marking of differential
signals and the differential impedance
- 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 SK
- 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 SK)
- 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 Type-C USB interface is
implemented, get the implementation verified by the relevant BU/PL
- 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 SK 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 affect the processor performance
- 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