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Microcontroller failure mode

Joaquin Gonzalez
Expert 1200 points

Dear all,

We would appreciate some help in this safety quetion.

We have the following scenario where there are two microcontrollers (SM320F28335EP and MSP430F249EP) supplied by two different DC/DC (regulating from 28V to 3.3V). If there is a failure at the internal circuitry of any of the DC/DC and the output is shorted to the input (so the output=input=28V), we would like to know if the microcontrollers can output 28V at their I/O pins when supplied at 28V or if these devices have any internal component limiting this failure mode.

Thanks in advance

Nuba.

  • Mastermind 7395 points

    If that danger exists, did you consider putting a crowbar circuit protection to cut off the voltage? Better that, than relying in what micros could do for you... they are not designed for that.

  • in reply to Avi Chami1
    Expert 1200 points

    Hi Albert,

    No I didn't consider that option.

    Also, I am not sure if the input-output shortcircuit  is a failure mode for a DC/DC as it is for a LDO.

    Any more feedback?

    Thanks in advance.

  • in reply to Joaquin Gonzalez
    Mastermind 7395 points

    It depends on the DC/DC type. SEPIC configuration cannot shortcut since it has a series capacitor. A transformer based configuration also won't easily shortcut input to output... unless a short between primary and secondary appears (I think that is rare). But buck converters failure mode can be a shortcut, if the switching FET fails. There will be a series coil between input and output.

    BTW regarding your previous question, 28V at the Vcc of a micro will almost certainly appear at the outputs.

  • in reply to Avi Chami1
    Expert 1200 points

    It is a buck converter, so I guess it is possible to happen.

    DOes anybody from texas know the answer about microcontroller protection against  overvoltage.

    Thanks in advance.

  • in reply to Joaquin Gonzalez
    TI__Guru 72115 points

    Hello Nuba,

    I do not know the specific microcontroller, but I expect that 28V is a lot higher than the absolute maximum rating of the input voltage of the microcontroller, correct?

    If this is the case, most probable the microcontroller will be damaged immediately and then it is not defined what is on the output pins of the microcontroller. If there is the risk of a damage of the DC/DC converter and you have to make sure that the rest of the system is not damaged, you need to make sure that the microcontroller never sees a voltage higher than the absolute maximum rating given in the datasheet.

    Best regards,
    Brigitte