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.
- I2C interface configuration, recommended connections and I2C interface
pullup.
- Slew rate requirements and connections for slew rate control.
- Open-drain output I2C interface connections when interface is not used.
- I2C instances and connection to multiple attached devices.
- Terminations for attached device address inputs.
Schematic Review
Follow the below list for the custom schematic
design:
- WKUP_I2C0 and MCU_I2C0 I2C interfaces (controllers) are complaint open-drain
output type IO buffers.
- During processor cold reset
and after reset, RX buffers are enabled, a pullup (4.7kΩ) is recommended
irrespective of IO configuration.
- During processor cold reset
and after reset, RX buffers are enabled, a pullup is recommended
irrespective of IO usage (including use case where I2C interface signals are
planned to be left as NC).
- The recommendation is to verify the pullup values used for the I2C
interfaces with the SK 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 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.