• State
  • Locked Locked
  • Replies 4 replies
  • Subscribers 31 subscribers
  • Views 1215 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

How to feed TAS5709 output to an follow up amplifier with common ground, headset or subwoofer

oscar jager
Prodigy 30 points
Other Parts Discussed in Thread: TAS5709

Hi,

If one wants to create an extra analog output signal for an amplifier, subwoofer or headset or a 2nd room amplifier then one typically has to deal with a common ground. 

However, the TAV5709 has a BTL output. In such a case I would normally use a following configuration. Take the plus outputs of both the channels (OutA and OutC) and offer  them as the left and right channel + signal. Then use the ground as common ground or - signal. 

Is there any risk is such configuration? 

Would it make sense to use a resistance and a capacitor before offering it as output to reduce power output and avoid dc current flowing to the ground ? If so, what are the recommendation for the resistance and res. capacitor ?

Thank you so much. 

Oscar

  • 0
    TI__Guru 57800 points

    Hi, Oscar, 


    Welcome to E2E, Thanks for your interest in our products!.

    The TAS5709 is a quite old Class-D amplifier and we have newer parts right now, actually, I think a DAC would be better for this kind of applications. Why don't you take a look to our PCM17xx family of Audio DACs?. 

    Do you have a special reason to use the TAS5709 in this application?, we don't test the functionality of this class-D amplifier in applications like this so we can't ensure the device will work as expected.

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer

  • 0 in reply to Diego Melendez
    Prodigy 30 points

    I just happen to get my hand on a charge of TAS5709 so that's we wanted to use them and we have already experience with it. So to us it seemed a simple solution. 

    The TAS5709 is normally used in BTL mode by using out A & B in inversed mode and so doubling the output power. The question is, could I use output A (and GND) only to drive a low power device like a head set or additional power amplifier. normally it should, but I'm not sure. I presume this must have been tested before when testing different configurations of the device. In fact, my only thing is, should I use a resistance (a small 8 ohm wouldn't harm nor take to much power away but should a DC flow from out A (or B, or C or D) to GND be avoided at all times. If so, I should put a condensator in serie with the connected headset output.

    BAsically it would look like this: (derived from TI reference configuration as in SLOU231c.pdf)


    -----------------------------FROM SLOU231c.pdf page 22 --------------------------

    outputA --------:L1:--------------------------OUT-A-----------|C?|--------(R?)----> new out A+
                                       _|_         __|__
                                      C29     C36/R10
                                       ----         --------
    GND____________|______|_____________________________> new out A- = GND

    -----------------------------FROM SLOU231c.pdf page 22 --------------------------

    C? I would like to avoid as it will change filter frequency at the low end. So the question is, would I need it or not If yes, I would have to take large `capacity to have lowest cut of frequency.
    R? I would probably take a few ohms only or skip it totally. Will test myself a bit. 

  • 0 in reply to oscar jager
    TI__Guru 57800 points

    Hi, Oscar,

    Theoretically you might be able to use the amplifier in the configuration you mention, however, you need to consider that the output signal from OutA has an offset of about ½PVDD, so C? should be populated to remove DC offset. As mentioned before, this is a Class-D audio amplifier that was not tested for applications like this so we can't guarantee that the device will perform as indicated in the datasheet. 

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer

  • 0 in reply to Diego Melendez
    Prodigy 30 points
    Hi Diego,
    I didn't realise the 1/2 PVDD, many thanks! That clarifies everything. Will test and may give you feedback in some time.
    Oscar