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Class D motor drive with analog input?

Brian Candiloro
Prodigy 30 points
Other Parts Discussed in Thread: TPA3112D1

We have been using class AB audio amplifiers for dc-coupled analog servo motor drive for years.  Now as we push for much smaller packaging, heat dissipation is a major issue.  I have been searching for a 15-20W, BTL, class D solution with ANALOG control input.  Can anyone point me to a device/family that might work for this type of application?

  • TI__Guru 55605 points

    Brian,

    Please take a look at the TPA3112D1.  Let me know if this doesn't make sense for you and we can go from there.

    http://www.ti.com/product/tpa3112d1

  • in reply to Ryan Kehr
    Prodigy 30 points

    Ryan,

    Thanks.  I had tried working my way through the selection guide and ended up with the TPA series which seemed like it would be worth digging into a bit more.  I was discouraged though by some of the comments in the audio forum about dc-coupling being a bad idea, and I was not sure how it would affect the bootstrapping, etc. 

    I have a little concern about the speaker guard technology triggering during normal operation, but since this a servo application, the input signal is likely to be small for long (slow) moves taking longer than the 420ms, and fast moves will involve a polarity change for accel/decel, so I guess that might just work out fine.

    Any tips on biasing the input signal to match the 3V expected on the inputs?

    Brian

  • in reply to Brian Candiloro
    Prodigy 30 points

    I'll try and ask this another way.  How do I correctly dc couple an analog signal that will typically be biased at something like VCC/2.  Is there an app note available?

  • in reply to Brian Candiloro
    TI__Guru 55605 points

    Brian,

    I am really sorry for leading you down the "garden path" here on the analog input audio amplifiers.  The input structure will not support a DC coupled input.  

    I am afraid that there are no parts in the line-up that do.

  • in reply to Ryan Kehr
    Prodigy 20 points

    Interesting, that was pretty much the exact same question I had. I find it hard to believe there isn't a way, but some Class AB devices were designed AC only as well. Presumably the problem is the DC bias level either can't be predicted or it varies?

  • in reply to Oliver Broad
    Prodigy 20 points

    I hope no-one minds me "bumping" this as it seems as if it would still be useful, I am still using Class AB pentawatt-package amplifiers as motor drivers, and I would still like to find a compact inexpensive "Class D" solution that could be dropped into an existing analogue system.

    The alternative would be to migrate the whole design to digital.