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TPA3255: Which DAC to use in BTL/PBTL mode - gain factor ?

Sebastian Wendt2
Prodigy 200 points

Part Number: TPA3255
Other Parts Discussed in Thread: PCM5121, , PCM5242

Hi,

we are using a PCM5121 DAC (2Vrms max output) and a TPS3255 in BTL mode.

When I output 2Vrms from the DAC and have 21.5dB Gain, I get ~24Vrms output voltage which results in 144W into 4 Ohms (this is also what I can measure).

But how can I reach higher output power - the TPA3255 product page says "The device is operated in AD-mode, and can drive up to 2 x 315 W into 4-Ω load at 10% THD and 2 x 150 W unclipped into 8-Ω load and features a 2 VRMS analog input interface"  but how does this work then ?

And using our setup, I can only achieve ~145W output power without clipping ?

Is there a gain setting I have to do ?

And does the TPA3255 change it's internal gain depending on the SE / BTL / PBTL mode ?

Or do I need a buffer op amp to reach higher output power e.g. in PBTL mode ?

Regards,

Sebastian

  • 0
    TI__Mastermind 19080 points

    Hi,

    I didn't find any description about gain setting on the datasheet. The only option is 21.5dB.

    So if higher output power is needed, you will need a higher input voltage. PCM5242 mentioned on datasheet is a 4.2-Vrms output device.

    Internal gain is not related with SE/BTL/PBTL configuration. These different configurations only affects how much power TPA3255 can deliver without clipping.

    Probably you can use another DAC with higher output voltage capability.

    Thanks!

    Regards,

    Hao

  • 0 in reply to Sam(MPAA) Zhang
    Prodigy 200 points

    Thanks Hao,

    PCM5242 is far too expensive and there is no other DAC with >2.1Vrms output.

    So we probably have to use a bunch of cheap opamps to raise the signal level between DAC and Amp :-(

    BTW - 2 VRMS is mentioned in the TPA3255 datasheet for being full compatible but actually it seems it isn't :-(

    Regards,

    Sebastian