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TAS3251: Pop noise

Danilo A.
Mastermind 26440 points
Part Number: TAS3251

Hi Team,

We received this inquiry from our customer.

I'm working on an amplifier system for a german pro audio company. Therefore we'd like to use a fully-digital signal path in combination with amps with digital inputs. We choose the TAS3251 as a candidate. We have our own design running for testing purposes.

The amp module is working without problems. The only thing is a pop noise after the init sequence, when the amp comes out of reset.

What is the correct startup sequence using the pins !DAC_mute, !RESET_Amp and I2C commands?
In the datasheet and the appnote concerning the process flows (SLAA799A) there are two different sequences described. Which one is the right one? How do the pins !DAC_mute, !RESET_Amp have to be integrated in the sequence?
In the appnote there is a pin !DAC_reset mentioned. Is that a typo?

He also added,

I tested the sequence described in the datasheet a few times. I still hear a short glitch from the speakers, when the output stage starts switching (exactly when I set the Reset_Amp pin high after the I2C init).

Pop and Click Free Startup and Shutdown 8.3.8:
I had a 33 nF Cap assembled on C_Start pin (because I use the same value as bootstrap cap). I also tested 100 nF, but that didn't change anything. When I increase the capacitance, will the ramp not be as steep?
Or would it be better to use a smaller value for C_Start e.g. the 10 nF which are recommended in the datasheet?
Can you send me a minimal init sequence (e.g. the register adresses and values) to be sure my code is working correctly?

Regards,

Danilo

  • 0
    TI__Expert 5410 points

    Hi Danilo.

    There are some things I need to check with our design team.

    I will reply you once I get the answers.

    BR.

    Wei Qiu.

  • 0 in reply to Wei Qiu
    TI__Mastermind 26440 points

    Hi Wei,

    May I ask for an update to this inquiry?

    Thanks,

    Danilo

  • 0 in reply to Danilo A.
    TI__Expert 5410 points

    Hi Danilo.

    I'm so sorry for replying to you late.

    As I checked with my team, the answers of your questions as below.

    Danilo A. said:
    In the datasheet and the appnote concerning the process flows (SLAA799A) there are two different sequences described. Which one is the right one? How do the pins !DAC_mute, !RESET_Amp have to be integrated in the sequence?

    A: Did the customer set it up according to the power-up sequence shown in the figure below? If there is still pop noise with this sequence, please retry steps 6 and 7 by swapping them. If there is still pop noise in the experimental results, please provide the test situation and experimental waveform. We will reproduce it on the EVM board to try to find the reason.

    Danilo A. said:
    How do the pins !DAC_mute, !RESET_Amp have to be integrated in the sequence?

    A: There are two mute modes for TAS3251. One is a hardware mute, which is implemented by pulling down the DAC_MUTE pin; the other is a software mute, which is implemented by modifying the value of the 0x03 register. Note: The priority of hardware mute is higher than that of software, that is, when using software unmute, you need to pull up the DAC_MUTE pin first.

    Danilo A. said:
    Or would it be better to use a smaller value for C_Start e.g. the 10 nF which are recommended in the datasheet?

    A: According to the description of datasheet, 10nF-470nF are all okay.

    BR.

    Wei Qiu.

  • 0 in reply to Wei Qiu
    TI__Mastermind 26440 points

    Hi Wei,

    Please see the response of our customer.

    I did a few more tests with the tas3251 hardware.
    I implemented the sequence exactly as described in your answer. I also tested to swap step 6 and 7, but that didn't change the issue.
    I hear the sound (not realy a pop noise, I'd either call it soft glitch) exactly after the pin RESET_AMP goes high, even if I hold the DAC in reset.
    That is not the first class-d amp I have developped and I also already worked with TI Chips (e.g. TAS 5707, 5731, 5825) and never had such issues.
    Do you have any further suggestion?

    Regards,

    Danilo

  • 0 in reply to Danilo A.
    TI__Expert 5410 points

    Hi Danilo.

    Could you ask customer to test DC offset as below. If test result is within the datasheet's range, the pop is normal. Because the pop is deeply related to DC offset. 

    Danilo A. said:
    TAS 5707, 5731, 5825

    These devices' DC offset is small, so they have small pop.

    BR.

    Wei Qiu.

  • 0 in reply to Wei Qiu
    TI__Mastermind 26440 points

    Hi Wei,

    Please see the feedback of our customer below.

    I checked the waveform of the output (after the LC filter). It is difficult to locate the small and short glitch precisely. See the foto below. Before the ramp-up of the amp output starts, there is something happening (like the gnd level is a bit over 0 V before and when the amp reset is pulled high the output level falls to 0 V).

    Regards,

    Danilo

  • 0 in reply to Danilo A.
    TI__Genius 14320 points

    HI Danilo

    Have you confirmed whether the DC offset within the range in the datasheet. you can use multimeter measure the DC voltage between OUTP and OUTN to confirm the DCoffset voltage.

    About the output waveform you confirmed, you just confirmed one pin output? or the difference voltage between OUTP and OUTN?

    thanks.

    jesse