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TMS320F28062: Unused ADCIN

Jens G
Expert 3185 points
Part Number: TMS320F28062

Hi C2000 Team,

In the DS of the F28062 is recommended (page 85):

"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."

 

What is the root cause for this behavior? What is the detailed Issue (higher current, software stall…)? What could happens if we not following this recommendations? Is there any risk analysis done? Background is that 1kOhm resistors need some space at the PCB and needs also a costlier routing. If it riskless possible to waive this?

 

Thanks!

  • 0
    TI__Guru 60865 points

    Hi Jens,

    The wording on this is a bit strong, but we are basically just recommending the resistor in order to limit the output current to be below the Io limit.  For all AIOs this is +/-4mA (see section 5.4 "Recommended Operating Conditions" in the datasheet).  If the AIO is erroneously enabled as an output, a 1K resistor would limit the current to approximately 3.3mA.  If the output current is exceeded for an extended period of time, the device could be permanently damaged.  

    The registers that enable the AIO and set the direction are EALLOW protected but don't appear to have lock bits.  The customer will have to decide if this is an acceptable risk.