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Question about Gain setting of TAS5754M and TAS5756M

Satoshi
Guru 19485 points
Other Parts Discussed in Thread: TAS5756M, TAS5754M, TAS5766M

Please let me know about Gain setting(Speaker Gain and DAC Gain) below,

①TAS5756M： Datasheet page53, table15

　Datasheet written in 26dBV and 20dBV Gain on table15, but EVM user's manual is 20dB and 14dB on page15～16, which is correct?

　I think that datasheet is including 6dB for internal DAC Gain, is it correct?

②Is internal DAC Gain fixed spec(6dB)?

　Or, is SPK_GAIN(20dB / 26dB) control from DAC Gain control? (Image is below.)

　・DAC Gain：0dB(1Vrms) + Amp Gain：+20dB(10Vrms) ＝ 20dB

　　　or

　・DAC Gain：+6dB(2Vrms) + Amp Gain：+14dB(10Vrms) ＝ 20dB

　　※Input is Full scale

③Is Gain setting depend on supply voltage?

④About Full scale DAC output(2Vrms), is this included internal 6dB Gain?

　ex)DAC Gain：+6dB(2Vrms), and Amp Gain：+20dB(20Vrms) ＝ 26dB

　　※Input is Full scale

⑤About register setting for Page1-Register2, which Gain setting for DAC Gain or AMP Gain?

⑥The datasheet of TAS5766, this Gain written in 20dB and 14dB.(datasheet page 41)

　Why differ from TAS5754M/5756M?

Best regards,

Satoshi

  • 0
    TI__Guru 57800 points

    Hi, Satoshi-san,

    As this is a closed loop amplifier the Gain of the TAS5754M and TAS5756M is set up in dBV units so the output is fixed to a certain value considering an input reference of 1 Volt. As the DAC has an output of 2V with full scale input, it is considered that the DAC adds 6dB to the total gain. 

    Please refer to my comments about your questions below:

    ① Correct, the information on the datasheet considers the total gain, including the DAC gain. The information on the EVM User's guide considers only the Amplifier's gain.

    ② The gain of the DAC is considered as +6dB because the output gain is referenced to 1V and the DAC has a full scale output of about 2V.  

    ③ This is a closed loop amplifier, so the gain is not dependent on the power supply. However, you must consider that the power supply level should be high enough to avoid the clipping of the output signal. 

    ④ Yes, the DAC gain is included in the gain spec from the datasheet.

    ⑤ DAC Gain; 0dB (+6dB from 1V reference) and -6dB (0dB from 1V reference).

    ⑥ The DAC gain is not considered in the TAS5766M datasheet.

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer

  • 0 in reply to Diego Melendez
    Guru 19485 points
    Diego-san

    Thank you for reply.
    About answer⑤, is there information for background of datasheet written 0dB and -6dB?
    (Rather than +6dB and 0dB)

    Best regards,
    Satoshi
  • 0 in reply to Satoshi
    TI__Guru 57800 points

    Hi, Satoshi-san,

    The DAC output of the TAS5754M is rated to have an output of 2 Vrms with Full scale input. The spec for the datasheet is considered from the perspective to have the option of changing the DAC output level between 2Vrms (0dB) or 1Vrms (-6dB) at full scale input. 

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer

  • 0 in reply to Diego Melendez
    Guru 19485 points

    Diego-san

    Thank you for many advice.

    Is below image correct?

    Best regards,

    Satoshi

  • 0 in reply to Satoshi
    TI__Guru 57800 points

    Hi, Satoshi-san,

    The image you sent seems correct, however I would suggest to refer to the gain setting of the amplifier in terms of  "dBV" instead of dB as specified in the datasheet.

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer

  • 0 in reply to Diego Melendez
    Guru 19485 points
    Diego-san

    Thank you for quick reply,

    Sorry for addition (maybe last question);
    About Figure 30 (TAS5754M datasheet P27) , which correct are unit of "AV(SPK_AMP)" dBv or dB?
    Customer think that correct is dB.

    Best regards,
    Satoshi
  • 0 in reply to Satoshi
    TI__Guru 57800 points

    Hi, Satoshi-san,

    The units are correct as they appear in the D/S, "dBV". This is because the data was captured using the default DAC gain setting, changing only the gain using SPK_GAIN pin.

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer