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TPA3250D2EVM: clarification on output power vs supply power and THD

Part Number: TPA3250D2EVM
Other Parts Discussed in Thread: TPA3245, TPA3250


1. From the datasheet's output power vs THD graph, it seems this chip in BTL mode, provides least noise for output of around 7w to 40w for 8 ohm load. 

        Now how do we run this EVM board in BTL mode, to output in the range of " 7w - 40w " per channel of stereo ? Do we need to limit the supply voltage from 15v to 24v? or is there any other way for maintaining low noise output power?

2. Apart from heat sink how TPA3250 differ from TPA3245? Both chip's output powers are very close to each other.

thanks and regards

S Sarath

  • Hi Sarath,

    You could control the input Vrms values so that your output is in the range of 7W - 40 W per channel instead of the supply voltage.

    Besides the differences in output power between the TPA3250 and the TPA3245 and one being a pad-down device while the other is a pad-up device, another huge difference is the supply voltages.

    Supply voltage ranges are:
    TPA3250: 12V-38V
    TPA3245: 12V-31.5V

    I hope this helps clarify things.

    Best Regards,

  • Hi Robert,

    Thanks for the reply.

    Could you please clarify the relationship between output power and supply voltage. From the data sheet graphs  it seems we need to maintain supply voltage under 24v to get output audio power under 40w.

    Would it be possible to get the graphs of output power vs THD noise for 8ohm loads when used in SE mode is. 4.0 mode. In data sheet only lower impedance load's graphs were provided.

    Regarding TPA3250 vs TPA3245 if we are powering it up with a power supply of 19v or 24v to keep the output audio power to under 40w , are there any other difference between them in terms of performance / scale / features ?

    Thanks and regards

    S Sarath

  • Hi Sarath,

    Let me clarify the output power vs supply voltage graphs. These graphs are showing the relationship between output power and supply voltage when you maintain a THD+N percentage of either 1% or 10%. So depending on what level of THD+N you would consider tolerable in your system will also greatly change what power levels you are able to achieve for a certain supply voltage.

    I can run the tests and send the results to you if you would like but I would need to know more about your system in order to do that.
    - LC filter values?
    - Supply voltage?
    - Is your input differential or single ended?

    Both of these devices are within the same family. High power and high efficiency. That said besides having different power levels I would say the biggest difference between, as mentioned before is needing a heat sink vs not. While the TPA3245 requires a heat sink, the TPA3250 is recommended to have more layers of copper pours for the PCB.

    Best Regards,

  • Hi Robert
    Wish you happy new year
    As of now I am looking for one of the evm boards for tpa32xx. And interested in its flexibility of using as 4.0 or 2.1 or 2.0 topologies.
    And to start with thinking to use laptop Power brick 19.5v 90w.
    1. Mostly the input signal would be single ended.
    2. How to use the evm boards for least THD + noise? Is 19.5v power supply good or do we need to use near max allowed voltage power supply?
    3. In the data sheet, 4.0 ie SE mode(8 ohm load graphs not given) is not having good THD + noise rating when compared with BTL or PBTL modes. If we need to use in SE 4.0 output mode what adjustment do we need to make ?

    Thanks and regards
    S sarath
  • Hi Sarath,

    Thanks for using the TPA32xx EVM boards!

    - For lowest noise performance I would recommend differential input, but this is not required and single-ended input will still provide good performance.
    - Using 19.5V is okay, but you will not be able to deliver the full power to the speaker. If you don't need the full power you should be okay. You can check if you need a higher voltage supply if you see the CLIP_OTW LED turning on frequently.
    - SE may require a power supply with less noise to reduce the noise on the output. Most of the noise is due to coupling with the PVDD power supply.