• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 31 subscribers
  • Views 200 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.

TPA3125D2: No load operation

James Hartvigsen
Prodigy 30 points
Part Number: TPA3125D2

I am designing a 5.1 channel audio system using 3 TPA3125D2 amplifiers. The subwoofer has it's own amplifier and will be driven directly from the preamp on my board, meaning that one of the channels will be driven with no load attached. There is also the possibility of other speaker combinations where one or both amplifiers on a given chip may have no load. Putting the unused amps into shutdown is not feasible as that would shut down both channels including the one being used. I have found conflicting information as to whether it is safe to run a class D amplifier with no load, with some saying that the output LC filter can create voltages high enough to damage the amplifier. Is it safe to run with no load attached, and if not then what can be done to make it safe? Is it as simple as placing schottky diodes from each output to the power rails to prevent the voltage generated by the filter from exceeding the power supply by more than one diode drop?

  • 0
    TI__Genius 17607 points

    Hey James, 

    The no load condition should be fine. You may even remove the LC filter if that channel is unused. However it is very important that you do not remove the channel's bootstrap capacitors to avoid faults. 

    I have heard the feedback from customers that the unused outputs get warm, to avoid this please place the device into HiZ/sleep when not in use (in this device it would be via /SD). 

    All the best, 
    Carolina 

  • 0 in reply to Caro Walter
    Prodigy 30 points

    Thank you for your reply. I believe you have answered my question, but I want to make sure that I understand correctly, if I may. I realized that I may not have adequately described my project. I am designing it with 3 dual channel amplifiers, and it can be configured in one of two ways.

    The first configuration is to use it as a 5.1 channel surround system. In this configuration one amp runs front left and right, the second amp runs surround left and right, and the third amp runs the center channel. On the third amp the second channel is unused, however I cannot place it into shutdown as that would also shutdown the center channel.

    The second configuration is to use it as 3 separate stereo channels. In this configuration one amp runs one stereo pair, the second amp runs another stereo pair, and the third amp runs a third stereo pair. Think of it as a multi-zone system that can feed 3 different audio sources to 3 different rooms in the house. In this configuration, I obviously need the output filter on all 6 amplifier channels.

    As you can see, removing the unused output filter is not an option, nor is placing the amplifier in shutdown. If I understand correctly, you say it is safe to run with no load with the only negative affect being that the output filter may get warm. I assume that most of this heat is being generated in the inductor. I am using an inductor that is rated for an ambient temperature of 85C and a maximum device temperature of 125C, so unless by "warm" you actually mean "very hot," I suspect (or at least hope) that will not be an issue.

  • 0 in reply to James Hartvigsen
    TI__Mastermind 19030 points

    Hi James,

    Got it. Pull low the SD will shutdown the 2 CHs, you can not only shutdown one CH by SD pin.

    If one CH is not used and LC filter can not be removed, you can short the input related to ground by switch control.

    Regards,

    Derek

  • 0 in reply to Yanming Gong
    Prodigy 30 points

    Perfect. I am already switching any unused channels to ground at the input to the preamp stages to reduce noise, so that should take care of it. Thank you.