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Digital input amplifiers maximum operating audio frequency

Philippe Junod
Prodigy 80 points
Other Parts Discussed in Thread: TAS5705, TAS5706, TAS5716, TAS5760M

Hi all,

I2S input power amplifier such as the TAS5705, 06, 16 have sampling frequencies configurable up to 192kHz. However, the maximum audio frequency is not specified.

I would like to know what is the maximum frequency the protocol can handle, given the sampling frequency. In addition, is there any frequency limit given by other artefact such as open or close loop technology?

I know there is at least two other discussions about this topic in this forum. Proposed solutions are PWM input circuits. I would like to understand I2S protocol limitations in ultrasound frequencies.

My application is ultrasound actuator control at 30 to 40 kHz. Output power is 10W. This application includes sinusoid carier generation and level control. Dynamic range is about 20 dB.

Thanks for your support,

 

Philippe Junod/ R&D engineer

 

 

  • 0
    TI__Guru**** 189399 points

    Hi, Philippe,

    Our closed-loop devices (TAS5706/16/anything with an even number) run out of loop gain before that frequency.

    Our open-loop devices do not suffer from this.

    -d2

  • 0 in reply to Don Dapkus
    Prodigy 80 points

    Hi Don,

    Your answer disqualifies the TAS5706 and TAS5716 because of closed loop technology.

    What about the TAS5705? Where can I get its maximum audio bandwidth given the highest sampling frequencies? What is the analog bandwidth limitation and what is the I2S protocol limitation (i.e. can we go up to fs/2) ?

    A second question for you: Is the even number staff also valid for analog input amplifiers such as the TPA3130? I expect not as it seems it can go over 60 kHz.

    I would appreciate to get qualification data for these circuits over the normal 20kHz limit in audio applications.

    Thanks for the answer and best regards, Philippe

  • 0 in reply to Philippe Junod
    TI__Guru**** 189399 points

    Hi, Philip,

    30-40 kHz isn't that far out, we shouldn't lose too much gain at that frequency, for the closed-loop amps.

    You might order an EVM and play with it to see if it meets your requirements.

    You will need to adjust the LC filter on the output to push it's 3 dB point out. Just be careful that the minimum of the filter impedance doesn't line up with the switching frequency. See section 5.1 of this app note on LC filter design.

    Unfortunately, this is not an area where we have characterized our devices.

    -d2

  • 0 in reply to Don Dapkus
    Prodigy 80 points

    Hi Don,

     

    EVM tests will be the second step in my selection process.

    First I need to select digital versus analog input (I prefer digital for system compactness). Then, the best circuit in term of reliability and performances.

    Overall voltage gain is not an issue as my application includes power monitoring and fine tuning, thus small gain drop is acceptable, although phase margin reduction may create instabilities.

    As I don't know anything on digital audio protocols, can you please help answering the question on frequency limit with 192kHz sampling rate in I2S processing?

    Thanks again for your support,

     

    Philippe

  • 0 in reply to Philippe Junod
    TI__Mastermind 22965 points

    Hi Philippe,

    If closed-loop amp is a preference, I would recommend using the recently released TAS5760x device family. It is a I2S input amplifier that can be used in either HW or SW control mode. Fs rates upto 96kHz are supported. (Note that there is no DSP processing option on these devices).

    Based on a quick test I ran, so using a 30K to 40K input should work fine.

    Here is a link to the datasheet of TAS5760M, the table on page-2 described the different package/device options.

    -Ravi

  • 0 in reply to Ravi Singh
    Prodigy 80 points

    Thank you Ravi for the test and feed back.

     

    I didn't catch this brand new circuit; it seems to be quite interesting in term of features and performances.

    About the closed-loop item, it was not recommended by Don because of voltage gain drop. However, if you tested it worked closed to Fs/2, it is promising.

    I will order an EVM to complete the evaluation.

     

    Best regards, Philippe