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DRV2667: DRV2667 outputting only 10V?

Drew Hamilton
Prodigy 60 points
Part Number: DRV2667

Hi,

I have been having on-again off-again problems with a circuit that is supposed to be driving a 100V Piezo. Recently I sent out for a new round of boards, and the I am getting 10V from the output. I cannot for the life of me understand why. Pardon the messy schematic, I've been scribbling on it as I work. You can see I am actually attempting to set the voltage around 91V.

I have tried playing around with different values for the feedback resistors but I am not getting the expected results.

Any help would be appreciated.

Thanks,

D

  • 0
    TI__Mastermind 18545 points

    Hello, 

    Your feedback resistors seem fine. Is the boost voltage stuck at 10V or just the output pins? In other words, is the boost able to reach 91V? 

    I noticed your Rext resistor sets the current limit at 1.28A but your boost inductor is rated for 1A. It would be best to replace the inductor with one that has a higher current rating. This would help the boost voltage stay steady when outputting to an actuator. 

    Lastly, in the layout, P$1 looks like a testpoint for measuring the boost voltage. Is that correct? 

    Best Regards, 

    Justin Beigel

  • 0 in reply to Justin Beigel
    Prodigy 60 points

    Hi Justin,

    Yes. Good eye. I had actually swapped out that Rext resistor already, and it doesn't seem to make much of a difference. I currently have it around 33k, but that doesn't seem to effect anything either way. Ibat_max is around 390mA in my design equations spreadsheet, so I didn't think that would be limiting the voltage. I have some new inductors on the way with 2A saturation current.

    When I scope Boost I am getting around 10V, so it seems that the boost is not working properly.

    -Drew

  • 0 in reply to Drew Hamilton
    TI__Mastermind 18545 points

    Hello, 

    While you wait for the new inductors to arrive, can you check if the boost is still at 10V if your piezo is not connected to the output? 

    Also, what is the load of your piezo and the frequency that you are using for your waveform? 

    Best Regards, 

    Justin Beigel

  • 0 in reply to Justin Beigel
    Prodigy 60 points

    Yes, the boost pin reads 10V with the Piezo disconnected.

  • 0 in reply to Drew Hamilton
    TI__Mastermind 18545 points

    Can you increase the boost capacitor to at least 0.1uF and see if you are still having the issue? The 0.02uF seems a bit low and might be part of the problem here. 

    Best Regards, 

    Justin Beigel