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AUXL maximum output Vrms swing for TWL6040

Naveen Kumar S
Intellectual 625 points
Other Parts Discussed in Thread: TWL6040, TWL6041

Hi All,

We are using AUXLP/AUXLN lineouts of TWL6040 to drive a Class D amplifier in our design.

In order to set the gain in this path to achieve 3.5W we have he following Queries:

(1)The power supply to PGA is 1.8V(from HSLDO)and -1.6V(from LSLDO).The maximum output swing from PGA can be within (1.8-(-1.6))=3.4V
Converting this to Vrms translates to ((3.4/2)/sqrt(2)) which will be 1.2V Vrms.
However, in "AUX-Output Path Specification" (Pg 23) for TWL6041(literature no: SWCS066C REVISED JANUARY 2012),
Output differential swing @ 0 dBFs,THD < -40 dB,RL = Typ is 1.7 Vrms(minimum).
How can we get this minimum of 1.7V Vrms with +1.8 and -1.6V supply?

(2)In the figure "Figure 4-11. Auxiliary Outputs" the gain at the output of PGA is shown to be 4.6dBVrms.Is this the maximum gain that can be achieved?

If yes, the output Vrms swing on AUX lineouts for this gain will be 1.7Vrms(4.8V peak to peak).How is this achieved with (1.8-(-1.6))=3.4V supply?

(3)In the register "HFLGAIN" we can program the gain in steps of 2dB (-52dB:6dB). Can you please corelate this with 4.6dBVrms gain in the Aux path.

Also,What is the maximum Vrms output available on AUXL lineouts(considering 6dB gain)?

Thanks and Regards,

Naveen

  • 0
    TI__Genius 9410 points

    Hello Naveen,

    I have moved this post to the PMU forum, where the TWLxxx parts are supported, to make sure the appropriate engineers address this.

    Please feel free to follow up if you do not get a timely response,

    Nate

  • 0 in reply to Nate Enos
    Intellectual 625 points

    Eagerly waiting for a reply.

    Thanks,

    Naveen

  • 0 in reply to Naveen Kumar S
    TI__Genius 9410 points

    Hello Naveen,

    I have reached out to the PMU team to follow up with them about this post. Moving the post could have disrupted the system, so I apologize for the inconvenience and we appreciate the patience.

    Thank you for the follow up,

    Nate

  • 0 in reply to Nate Enos
    Intellectual 625 points

    Hi, 

    Waiting for a response.

    Thanks & Regards,

    Naveen

  • 0 in reply to Naveen Kumar S
    TI__Intellectual 1915 points

    Hi, I'm working on this request; I have contacted the design team to get an accurate answer. I'll let you know when I have their feedback.

    Best regards, Alain.

  • 0 in reply to AlainC
    TI__Intellectual 1915 points

    Sorry for the delay: here you are:

    We are using AUXLP/AUXLN lineouts of TWL6040to drive a Class D amplifier in our design.[...] How can we get this minimum of 1.7V Vrms with +1.8 and -1.6V supply?

    Answer: AUXLN/AUXLP are differential outputs so overall maximum swing is VDD-VSS=3.4V on positive alternance and VSS-VDD=-3.4V on negative one i.e. +/-3.4V which translates into 2.4Vrms.

    In the figure "Figure 4-11. Auxiliary Outputs" the gain at the output of PGA is shown to be 4.6dBVrms.Is this the maximum gain that can be achieved?

    Yes as output can go up and above 1.7Vrms in differential mode.

    In the register "HFLGAIN" we can program the gain in steps of 2dB (-52dB:6dB). Can you please correlate this with 4.6dBVrms gain in the Aux path. Also,What is the maximum Vrms output available on AUXL lineouts(considering 6dB gain)?

    The PGA can support gains up to 6dB. However the maximum swing with 1% distortion is specified at 1.7Vrms or 4.6dBVrms. To achieve this swing with best SNR, one creates maximum swing at HFDAC as seen in figure below (i.e. 2.6dBVrms):

    The maximum Vrms output on AUXL is 1.7Vrms to be within 1% distorsion.

    Hope this helps, Alain.

  • 0 in reply to AlainC
    Intellectual 625 points

    Thanks for the clear answers Alain. It was very helpful.