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Class-D amp for 1-2 ohm loads?

Other Parts Discussed in Thread: TPA3112D1, TPA3100D2, TPA3123D2

I have to drive  1 to 2 ohms on an audio chanel.

The most audio class d amplificators are 4 ohm or 8 ohm.  Is it possible to link (to twin) two output of a double chanel ampli.

(or other idea)

Patrice

 

 

  • Patrice,

    Yes, it is possible. This mode is called Parallel Bridge-Tied Load (PBTL). For example, refer to the data sheet for our TPA3112d1. On page 14, you can see that the outputs have been tied together to allow for a smaller load. All two-channel BTL amplifiers are capable of doing PBTL after the LC filter, but this part is designed to be able to do PBTL before the filter.

    Please let me know if you have any additional questions.

    - Nate

  • Thanks Nate for your answer

     

    I  take a 20w stereo class d as TPA3100D2 . In the data sheet it can output 15W/ch 4 ohms. If i do the BTL link, do i can have 30W in a single chanel of 2 ohms.

    Is there a limite to put 2 x TPA3100D2 in BTL to have 60W in 1 ohm ?

    Is there a btl schematic.

    Patrice

     

  • Hi Patrice,

    Yes it is possible. I have hooked it up myself today. A few things you will want to consider:


    1) We cannot guarantee the life of the part when run at this current level. It is well above normal use.

    2) Due to process variations, you are running the risk of two parts not functioning together correctly because of mismatched gains or DC offset differences. I couldn't tell you what the chances are of this happening. Martin Haag, a member and poster on these forums, has been doing this for a while without issue. THe TPA3100D2 is one of our better parts at matching in this way, but it's still something to be aware of.

    As for the schematic, I used our EVMs and ran one as slave, the other as master. I also shorted their clocks together via the test point. I shorted RIN on one board to RIN on the other and same for LINs. I shorted all of the + outputs together and all of the - outputs and connected a 1ohm load. If you're using our EVMs for testing, be aware that the RCAs used on this board are self-shorting. This means that they short the input to GND if the jumper is installed and no RCA input is connected, so be aware that you'll have to insert something in the RCA jacks if there's not something in there already.

    To put it simply, you can do it, but we can't guarantee it'll work across all scenarios.

    - Nate

  • Hi Nate,

    I will keep with only one ampli.

    Perhaps the limitation to a lower load is the current limitation .

    So is it possible to have a lower load if i limit the input . I mean , if the product is limited to 10W it could drive (1.58 A /6.32V rms  on 4 ohm) or  it could drive (2.23 A/4.47Vrms on 2 ohm) or it could drive (3.16 A/3.16Vrms on 1 ohm). The short circuit protection limit probably this but with witch value ?

    Where is it possible to find the value of the over current limitation.

    I have tried the TPA3113 in PBTL mode. I don't find this value of current limitation in data sheet.

    I would want to know it for the TPA 3100 or TPA3110. Is it the same if the amplifier is a stereo in pbtl mode or mono with more power ?

    Patrice

     

     

     

  • Patrice,

    The limitation to a lower load is definitely a current limitation.

    We don't put over current protection numbers on data sheets because we can't guarantee the exact number like other specifications. The purpose of OCP is to protect the part in a true short circuit situation. In any kind of sustained operation, you will push the thermal limits of the part way before you get close to OCP due to the heat created from the losses in the power stage.

    At any rate, here are the OCP numbers for the two parts:

    TPA3100 shuts off at about 6A

    TPA3110 shuts off at about 5A

     

    Again, these can vary a bit over specific processes, and they're meant to protect the part from being damaged during a short circuit event. You will always hit the thermal limit before hitting the OCP limit in normal operation.

    Please let me know if I can help further.

    - Nate

  • Dear Nate,

    I am testing TPA3123d2. 

    If I connected TPA3123d2 in BTL mode, may I connect the output to 2 ohm load (I mean, connect four 8 ohm speakers in parallel) without SCP?

     

    Thanks.

    Regards,

    Eddie