General
Review and verify the following for the custom
schematic design:
- The sections
above, 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 or EMC 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.
- 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 list below 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 the USB Type-C®
interface is implemented, get the implementation verified by
the relevant BU or 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 to the 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.