Because of the Thanksgiving holiday in the U.S., TI E2E™ design support forum responses may be delayed from November 25 through December 2. Thank you for your patience.

  • State TI Thinks Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 2 answers
  • Subscribers 31 subscribers
  • Views 754 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TAS5614LA: Use of PWM inputs

ajayt
Genius 9555 points
Part Number: TAS5614LA

When we use the TAS5614LA (or any of the other class D amp chips), we have found a way to get around this issue for the time being but someone has asked me to check that it’s fine to do this.

 

With the TAS5614LA, I can set all 3 mode pins low, setting it to be 2 x BTL with each of the two channels taking two PWM signals.

 

 

When I used this mode before, I always set Input A and Input B to be the inverse of each other (and the same for inputs C and D). To fix it, I set inputs B and C to a constant 50% duty ratio, and control Input A and Input D as before.

 

Can I just check that it’s OK to do this, and will not cause the chip to operate in a way that was not intended? I expect this is OK since in this mode it does allow four separate PWM inputs, but I’ve been asked just to check this is OK so it’s not something we need to be nervous about.

 

Thanks,

 

  • 0
    TI__Expert 6295 points
    this config sounds ok for me. But we can get Robert to help double confirm back to you
  • 0 in reply to Xiaolin Qin
    TI__Mastermind 23650 points

    Hi Ajayt,

    This sounds like you are wanting to run the device in BD mode rather than AD mode. As shown in the mode settings below, if you are running BTL BD mode then you will want to have M3 and M1 low and make M2 high. Best Regards,

    Robert Clifton

  • 0 in reply to ajayt
    TI__Mastermind 23650 points
    Hi Ajayt,

    Thank you for the helping me understand what you are doing. I guess my biggest question is why not just use the single PWM input signal in AD mode for BTL?

    Regards,
    Robert Clifton
  • 0 in reply to Robert Clifton56
    TI__Genius 9555 points

    The issue is that I want these signals at the output of the power amp (one side of the drive changing PWM to drive the load, the other side fixed at 50%).

     

    Looking at the video here:

    https://e2e.ti.com/support/audio/f/6/t/768489

     

    There is a cross-coupling effect between channels B and C, so as a workaround I want the power amp to drive the following outputs:

     

    BTL Channel 1

    OUT_A

    Normal drive

    OUT_B

    Constant 50% drive

     

     

     

    BTL Channel 2

    OUT_C

    Constant 50% drive

    OUT_D

    Normal drive

     

    Since OUT_C and OUT_D are the same, there is no cross-coupling effect.

     

    I want to be able to set the inputs to achieve this. If I set the amp up to just use a single PWM input, would these outputs be achieved?

     

    If possible, I would prefer not to change the settings of the mode pins as my board has pins M1, M2 and M3 all hard-wired to GND. However, I have absolute control of the 4 input PWM signals so these can be set quite easily to the following:

     

    INPUT_A

    Normal drive

    INPUT_B

    Constant 50% drive

     

     

    INPUT_C

    Constant 50% drive

    INPUT_D

    Normal drive

     

    I realise this may be an unusual setup, but testing has shown that it works fairly well. It drives the outputs and the cross-coupling effect is gone. I just want to know that it’s safe to operate like this, and that I’m not operating the power amp chip in some way that should not really happen. Can you confirm that this is the case?

     

  • 0 in reply to ajayt
    TI__Mastermind 23650 points
    Hi Ajayt,

    Firstly I want to ask if you have been testing this on the EVM or a customer board?

    Now the way I'm seeing how you're running this device seems to create a sudo SE output configuration without the need of a DC blocking capacitor since the 50% constant drive FETs will act like a DC reference point. This might be ok to operate the device in but I cannot 100% guarantee this since it's not promised in the datasheet.

    Also are you seeing any reduction in output power from driving the device like this versus standard AD mode?

    Regards,
    Robert Clifton