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SN74HCS541: safety documentation, guaranteed low output under failure

Ue
Genius 16485 points
Part Number: SN74HCS541

Hi all

My customer has an industrial motor control application where they have to implement a safety feature called "safe torque off".

Here they are looking for a buffer where they can guarantee that the output will be low if the device fails / is damaged.

This will make sure the PWM-signals driving the motor H-bridges will be guaranteed off in case of a device failure.

Do you have an idea how to solve this ?

Do we have safety documentation for logic functions that could be helpful ?

Best regards

Ueli

  • 0
    TI__Guru* 96681 points

    Hi Ueli,

    We don't offer any logic devices with a guaranteed failure state. I haven't ever seen one on the market, either. We only guarantee operation within the recommended operating conditions.

    Ue said:
    This will make sure the PWM-signals driving the motor H-bridges will be guaranteed off in case of a device failure.

    How are they expecting to detect a device failure -- and which device are they expecting to fail? What constitutes a failure? How is it expected to fail? From what?

  • 0 in reply to Emrys Maier
    TI__Genius 16485 points

    Hi Emrys

    Thank you for the quick reply. For "safe torque off" there are certain requirements specified, meaning you have to demonstrate that this function still works even if one device fails. 

    It is a particular problem and designing the circuit can be challenging.

    You might have to introduce some redundancy in your design.

    Best regards

    Ueli

  • 0 in reply to Ue
    TI__Guru* 96681 points
    Ue said:
    You might have to introduce some redundancy in your design.

    I agree, but that won't eliminate all possible issues. For example, if a device fails as a short from VCC to GND, their whole system will be killed.

    In my experience, failures in logic devices are caused by misuse (what we usually call EOS, or electrical overstress) - exceeding values in the abs max table. I would recommend they focus on avoiding specific failure conditions, and then focus on those they can't avoid.

    If we have more details regarding which failure modes they expect -- for example, connecting 600V to the output by accident -- then I can provide more details on what I'd expect the device to do under those circumstances.

    As proposed currently, I can't possibly provide any useful feedback.