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DRV2605L: H-bridge failure fault detection

Elliott Berg
Prodigy 20 points
Part Number: DRV2605L

Our application requires stringent safety precautions. It uses a Precision Microdrives C08-00A LRA (32.6 ohms) device, driven by a DRV2605L, powered from a 5.0V supply. Ideally, we need to detect a fault condition where the DRV2605L H-bridge fails to commutate, applying 5 volts continuously across the 1.2V-rated actuator, thereby causing it to overheat.

I note that Actuator Diagnostics detects open- or short-circuit actuators. However, it would simplify my design if it could also detect the above static output state. My question being, is there a way of using back-EMF (or some other parameter) in closed-loop mode to detect such a fault?

  • 0
    TI__Guru* 84915 points

    Hi, Elliott,

    Welcome to E2E and thank you for your interest in our products!

    As you mentioned, the actuator diagnostics feature is used to detect if the actuator is open or shorted. As mentioned in section 8.3.2.6 the DIAG_RESULT bit shows the result.

    In addition, the DRV2605L has some protection features whose result is included in some registers flags.Thermal protection and overcurrent protection are some examples of protection features with flag ( see section 8.3.12 for more details: http://www.ti.com/lit/ds/symlink/drv2605l.pdf#page=19 ). The regulator is also protected against overcurrent events.

    Besides these detection features, I think there are no more other functions to monitor the actuator behavior.

    Please let me know if you have additional questions or comments on this. We will be glad to help you.

    Best regards,
    Luis Fernando Rodríguez S.

  • 0 in reply to Luis Fernando Rodriguez S.
    Prodigy 20 points

    Hi Luis,

    Could you please check the following:

    On page 57 of the DRV2605L data sheet, 9.2.2.1.2.1 states that "The auto resonance engine accomplishes this tracking by constantly monitoring the back-EMF of the actuator.". At 8.6.25, bit 5 LRA_AUTO_OPEN_LOOP is set to 1 if a back-EMF signal is not detected (LRA only).

    Also, paragraph 8.3.2.5 states that "In the event where the automatic level-calibration routine fails, the DIAG_RESULT bit in register 0x00 is asserted to flag the problem."

    Then in 8.6.1, bit 3 DIAG_RESULT is set to 1 in Diagnostic mode if "Actuator is not present or is shorted, timing out, or giving out–of-range back-EMF".

    Again, in 8.6.19 A_CAL_BEMF[7:0] would surely be invalid if the actuator were permanently driven in one direction, as there would be no back-EMF.

    I am not a programmer but but could any of the above be used to flag the H-bridge fault I described? If so, my programmer colleague should be able to implement such a test and cut the power to the device, making it fail-safe. Which test/register do you think would be the most effective?

    Thanks,

    Elliott.

  • 0 in reply to Elliott Berg
    TI__Guru* 84915 points

    Hi, Elliott,

    Thank you for providing additional information about this.

    I don't think there's a specific flag to detect the problem that you mentioned. However, the suggestion that you mentioned about the LRA_AUTO_OPEN_LOOP bit could be used for this case. I think your problem could be associated to a wrong back-EMF or a bad response from the actuator. When the back-EMF is not detected, the device would change to open-loop automatically. You would need to use the bit 0 of register 0x1D as a flag to detect if the device didn't receive a back-EMF response.

    I hope this make sense. Please let me know if you have additional questions or comments on this.

    Best regards,
    Luis Fernando Rodríguez S.