General
Review and verify the following for the custom
schematic design:
- Reviewed above "Common checklist for all
sections" section of the user's guide
- Timing and switching characteristics, and any additional
information available.
- Mapping of processor pin (ball number) to the required
functionality (peripheral, signal name) on custom board
(selected pin supports muxing (multiplex) the IO for the
required function) and naming of the signal as per the
processor data-sheet pin attributes signal name column (when
using standard peripherals).
- Matching of the polarity of the peripheral data interface
signals between the processor and the attached device
(Example Mapping of Data, Clock or similar connections)
- Open-Drain output
buffer type I2C interface instance (I2C2, can be configured
to use LVCMOS buffer type) supported and connection to
multiple attached devices.
- Open-Drain output
buffer type I2C interface configuration, I2C interface
pullup requirements and connection recommendations.
- Slew rate requirements and connection of RC (C near to processor
pin) for slew rate control when pulled to 3.3V supply.
- Connection of attached device address inputs
- Open-drain output type buffer I2C interface Fail-safe operation
support
- Addition of required bulk and high frequency capacitors, and
value
- Open-drain output type I2C interface connection recommendations
when interface is not used.
- Voltage connection of the pullup to support Hs-mode (up to
3.4Mbps is supported when pulled to 1.8V)
Schematic Review
Follow the below list for the custom schematic
design:
- I2C2 (only when
using processor pins with "I2C OD FS" Buffer Type. Example:
B8, D8 for ANB package) controllers have dedicated I2C
compliant open-drain output type buffers.
- A pullup is
required only when the IO is used as I2C interface or IO
interface. I2C interface signals can be left unconnected
when IO is not used.
- The
recommendation is to verify the pullup values used for the
I2C interface with the EVM schematic implementation or
calculate the pullup value based on the load. A pullup
(4.7kΩ, adjust after testing) is recommended for the I2C
interfaces.
- The I2C pullup supply voltage connected follows the steady-state
maximum voltage specified for fail-safe IOs. The supply
threshold depends on the supply voltage connected to IO
supply for IO group.
- RC for open-drain output type IO buffer for limiting the input
slew rate when interface operates (pulled) at 3.3V.
Capacitor connected near to the processor I2C interface pins
when RC for input slew rate control is implemented. Verify
the effect of RC on the I2C interface speed and adjust the
RC as required.
- Supply rails connected to the IO supply for IO group VDDSHVx or
VDDSx referenced to (powered by) I2C peripherals and
attached devices IO supply are sourced from the same supply
and follow ROC.
- Attached device
address inputs connected to IO supply through a resistor
(> 1kΩ).
- Processor supports multiple I2C instances. The recommendation is
to verify that there are no I2C address conflicts on any of
the I2C interface. In case additional I2C interfaces are
required, an I2C switch can be used.
Additional
- The
recommendation is to review the Timing and switching
characteristics, I2C Exceptions section
of the processor-specific data sheet during the design stage
and include the required circuit.
- The I2C bus can
only be operated as fast as the slowest peripheral on the
bus. If faster operation is required, move the slow devices
to another I2C port.
- The
recommendation is to not place more than one set of pullup
resistors on the I2C bus, the pullups can result in
excessive loading and potential incorrect operation. Adjust
the pullup value based on the bus speed configured.
- The
recommendation is to make sure IO supply for IO group
powering the processor I2C IOs matches the supply voltage
used for the pullup and the attached I2C devices IO supply.
Connecting the pullups to proper supply level can prevent
incorrect I2C interface operation.
- I2C interfaces
support clock stretching. The recommendation is to adjust
the pullup in case the measured clock frequency does not
match the configured frequency due to the bus loading or
signal slew rate.