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Class AB single ended output question

Marvel52
Prodigy 200 points
Other Parts Discussed in Thread: TPA0233, TPA0211, TPA2010D1, TPA6211A1, TPA2011D1, TPA6138A2

Hello All,

I am designing the final audio amp stage for a system with a 3.4volt  single supply . The input needs to be mono, single ended ~line level. Output needs to be  >1 watt  into 4 or 8 Ohm onboard speaker with the ability to plug in/switch to an external speaker/headset via external audio jack with no less than half power of the onboard speaker. The problem that I'm having is that the type of external speaker device required has one end of the speaker tied to ground due to other functionality within the connection and device and it is not cost effective to isolate ground or use another type of external speaker/device for this application. the TPA0233 seems just about right but a little low on power I need help with understanding some details about the TPA0233 and any other options that may be more suitible to my application. The internal speaker could use a Class-D amp but the external speaker could be up to 6' (wire length) away from the amp in addition to the speaker being ground referenced.

Can 1 single ended input be used for both BTL and Headphone modes on TPA0233?  

Is there a higher wattage amplifier with functionality/Vcc  similar to TPA0233 ?

Is there a simple way to capacitively couple the audio out to the ground referenced external speaker and still use a Class-AB differential amp without a headphone mode?

Should i be concerned about the distance of the external speaker as far as using a Class-D? and if not is there an efficient way to couple a Class-D to a ground referenced external speaker? If yes to these, what Class-D would you recommend?

Summary: 3.4 Volt single supply, single ended ~line level input, 1 Watt audio output required, Mono output to internal speaker "floating" 4 or 8 Ohm or external speaker - referenced to power supply/signal ground(within external speaker device). 

Thanks for reading.

  • 0
    TI__Guru** 102375 points
    Hi,

    Is TPA0211 better for your application? This is a mono amplifier with SE input for both BTL and SE output.
    Is there a chance that your application could use two amplifiers, one for the internal speaker and one for the external speaker?

    Best regards,
    -Ivan Salazar
    Texas Instruments
  • 0 in reply to Ivan Salazar
    Prodigy 200 points
    Ivan,
    The TPA0211 is closer to what I am looking for. The mono input and price range look good but still doesn't solve the external SE speaker issue with adequate power (SE output only 170 mw into 8 Ohms at 3.4 volts).

    In considering your suggestion of using separate amps the question I would have is does TI have any SE in/out audio amplifiers that can output >.5 Watts with a 3.4 Volt supply? I.e. is this even technically possible?

    Assuming I can get the external speaker ungrounded in a cost effective manner and use a Class-D amp for internal speaker as well as 4-32 Ohm external speaker or earpiece/headphone I have the following questions about Class-D.

    Is there a class D that can drive 4-32 Ohm speakers? and if so what would be a good ic to look at for 3.4 volt supply with > 1 watt at 4 Ohm speaker?

    What is the maximum length of say 26GA wire from amplifier to load for typical class D?


    Thanks
    Eric
  • 0 in reply to Marvel52
    TI__Guru** 102375 points
    Hi Eric,

    In your application both speakers (internal/external) will be rated with the same impedance? Or these could be any speaker from 4 to 32 Ohms?
    You need both amplifiers with SE output?
    If you're able to use BTL output, you could look into AB or D amplifiers. Low power amplifiers are normally rated for loads from 4 to 8 Ohms and headphone amplifiers are rated from 16 to 32 Ohm.
    According to the summary in your original post, you're looking for 3.4V supply, mono SE input, 1W for internal BTL speaker (4 to 8 Ohm) and 1W for external SE speaker (4 to 32Ohm)? I will look for suggestions with a two-IC combination.

    Best regards,
    -Ivan Salazar
    Texas Instruments
  • 0 in reply to Ivan Salazar
    Prodigy 200 points
    Hi Ivan,

    Internal speaker will be either 4 or 8 Ohms, >=1 Watt depending on best match for s/n and amplifier used. External speaker could be 4 to 32 Ohms, .5 to 1 Watt I.e. we would expect close to 1 watt @ 4 Ohms, ~ .5 watt @ 8 Ohms and so forth up to 32 Ohms. One side of external speaker will be grounded. Internal and external speaker amps will need to run from a single 3.4 Volt supply.

    The reason I am asking about wire length and Class-D is the external speaker/device could be a speaker mic with only a 4 pin connection ground, push to talk, mic audio +, and speaker audio+. I have considered building a circuit that will dereference ground from the external speaker device(temporarily turning ground output into the other side of BTL speaker output ) when it is in "speaker" mode and then re-connecting ground while simultaneously disconnecting the amplifier power and output when the external speaker device(speaker mic) is using its ground referenced components. This would potentially allow us to use only one amplifier for the whole device which would reduce cost. That is why I need to know about the feasibility of a Class-D driving 4 to 32 Ohm loads and any wire length issues(from my previous question), so that I can see if it even makes sense to pursue this ground dereference concept.

    Thanks
    Eric
  • 0 in reply to Marvel52
    TI__Guru** 102375 points
    Hi Eric,

    For the internal speaker you can use most of our low power Class AB/D amplifiers, some of them are TPA6211A1, TPA2011D1 and TPA2010D1. These are mono amplifiers with BTL output, rated for 4/8 Ohm loads. TPA6211A1 is AB and TPA2011D1/TPA2010D1 are D. Our low power AB and D amplifiers have BTL output. Unfortunately there aren't low power Class D amplifiers with SE output.
    Class D amplifiers are not recommended for applications that require long length wires because these wires can become antennas. Besides, these amplifiers require inductor filtering at the output.

    For the external speaker you could take a look at headphone amplifiers like TPA6138A2. Headphone amplifiers are rated for higher impedance loads and these are stereo amplifiers, you may need to left one channel unused. These amplifiers have SE outputs.

    Best regards,
    -Ivan Salazar
    Texas Instruments