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TMS320F28035: How to design external circuit for AIO?

Aki Li
Genius 10115 points

Part Number: TMS320F28035

Customer wants to use AIO function due to limited GPIO amount with F28035. There is one statement in the datasheet:

Unused ADCIN pins that are multiplexed with AIO function should not be directly connected to analog ground. They should be grounded through a 1-kΩ resistor. This is to prevent an errant code from configuring these pins as AIO outputs and driving grounded pins to a logic-high state.

Could you give some suggestion on the hardware design if using AIO function for input or output? As we know, it might impact the performance of the analog peripherals due to noise coupling. Thank you.

  • 0
    TI__Guru 62975 points

    Aki,

    As you have mentioned, the AIOs will be referenced to the analog VDDA and VSSA supplies so there is the potential for AIO noise to affect the ADC performance.  If possible, use the AIOs for signals with the least amount of expected toggling (for example, a FAULT indicator).  Extra attention should be given to the AIO return paths, especially if there are split analog and ground planes.  There are no hard requirements, but I recommend using series resistors to dampen the digital signal switching.

    The 1kΩ resistor is meant to mitigate an unintended short from an active AIO output to a supply.  This really applies to any output signal in general.  I think this specific wording may have been added by special request to satisfy an external customer's documentation needs.

    -Tommy

  • 0 in reply to tlee
    TI__Genius 10115 points

    Thank you!