TAS5614LA: Use of PWM inputs

ajayt

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,

over 5 years ago

0 Xiaolin Qin over 5 years ago

TI__Expert 6295 points

this config sounds ok for me. But we can get Robert to help double confirm back to you

0 Robert Clifton56 over 5 years ago in reply to Xiaolin Qin

TI__Mastermind 20830 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 ajayt over 5 years ago in reply to Robert Clifton56

TI__Genius 9555 points

TAS.docx

0 Robert Clifton56 over 5 years ago in reply to ajayt

TI__Mastermind 20830 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 ajayt over 5 years ago 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
BTL Channel 1	OUT_B	Constant 50% drive

BTL Channel 2	OUT_C	Constant 50% drive
BTL Channel 2	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 Robert Clifton56 over 5 years ago in reply to ajayt

TI__Mastermind 20830 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

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TAS5614LA: Use of PWM inputs