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DRV2667: Failure of switch inductor

Steve Allen
Prodigy 70 points
Part Number: DRV2667

Having some issues with the DRV2667 and trying to narrow down potential causes.  I'm thinking the switch inductor is sized to small; the device is rated to 1.8A and the drive current (Rext) resistor is set to 1.8A (8.87k).  We are having some failures of the inductor but still debugging to see if this is really the case.  On failed units if the inductor is replaced the device functions normally again.  We've had less than 5% failure.  I've left the In+ and In- inputs floating, by thoughts are these should be tied off to ground or vdd, any suggestions?

  • 0
    TI__Guru* 84915 points

    Hi, Steve,

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

    Could you share the circuit schematic in order to have a better approach to this issue?

    In addition, do you know if the failure boards/units fail again after the inductor replacement? Does a higher current inductor solve the problem if it fails again?

    Any other information you have about this issue will be really appreciated.

    Thank you.

    Best regards,
    Luis Fernando Rodríguez S.

  • 0 in reply to Luis Fernando Rodriguez S.
    Prodigy 50 points

    Hi Luis,

    I've been working with Steve on this issue and can answer your questions.  

    So far we have identified three failure types:

    • Failure on initial inspection
    • Failure after 3-5 hours (not continuous use) of working normally
    • Works normally for a few minutes, then it begins saturating. After a short while (a few milliseconds to minutes), the output returns to normal.  See picture below

    On failed units, the output voltage of the haptic driver appears saturated and the inductor gets very hot (up to 107°C) after a few minutes of use.  Most units that are saturating cannot go higher than about 11Vpp (expected value is 50Vpp), but one unit began saturating at 30Vpp. On normal units, the temperature of the inductor is approx. 52°C. 

    When the inductor was replaced (with one rated for 1.8A), the output returned to normal and the temperature of the inductor was the same as one on a normal unit. The failed unit with a new inductor has not failed again after more than 6 hours of use. I have removed the inductor from a failed unit and placed it on a functional unit - this caused the functional unit to fail.  We are using a 3.3µH Murata Electronics inductor (https://www.digikey.com/product-detail/en/murata-electronics/1277AS-H-3R3M=P2/490-10593-1-ND/6164579). As of now, no units have failed after the inductor has been replaced.

    The solder joints of all parts look ok and the values of all passive components (except the inductor) have been verified. I have attached the circuit schematic for you to review.

  • 0 in reply to Farrell Brown
    TI__Guru* 84915 points

    Hi, Farrell,

    Thank you for your feedback on this.

    I have few observations regarding the inductor that you are using. Particularly the current limit and the current supported by the inductor. It seems that you have selected a current limit of ~1.78A. This value is near of the supported current of the inductor. So, I would recommend to choose an inductor with higher current capabilities or to reduce the current limit with a higher Rext resistor. All your information makes me think that all is associated to the maximum limits of the inductor.

    Please let me know what you think and if you have additional questions or comments on this.

    Best regards,
    Luis Fernando Rodríguez S.