TPA3221: Feedback on driving 2 ohm in BTL

M.A.M

Part Number: TPA3221

Hi,

My customer would like feedback to their tests:

"We tried to do some testing with our supplier on the TPA3221 evaluation board with 16.8V Vcc, 2ohm resistor load, BTL. 1KHz signal.

It seems that the peak voltage we measured at the speaker output is about 14.5V.
I scan in the spec, there is no Plimit setting, I would expect the peak voltage to be close to 16V.

Is this normal to have 14.5V as we have measured ?

We are still 2A away from the OCP of 10A and we would need just a few cycle of peak power.

1) Please confirm if our finding is correct.

2) Also, would you be able to share the efficiency curve for 16V, 2 ohm, BTL configuration ?"

Thanks for looking into this, and maybe suggest alternative output inductors to use on the EVM.
B.r M.A.M

over 6 years ago

0 Dylan Yao over 6 years ago

TI__Genius 10870 points

Hi,

Robert will follow up with you soon.

Dylan

0 Robert Clifton56 over 6 years ago in reply to Dylan Yao

TI__Mastermind 27590 points

Hi M.A.M,

Have you taken the impedance of the inductor in the LC filter into consideration? It's possible that if the impedance is high in the inductor it could be causing a bit of a voltage drop on the output.

Regards,
Robert Clifton

0 M.A.M over 6 years ago in reply to Robert Clifton56

TI__Expert 8805 points

Yes, for the EVM the total DC resistance of the 2 FETs and 2 inductors sum up to 0.19 ohm so with 16.8V the voltage over a 2 ohm load it should be 15.34V seen across the load.
Would you say that the remaining drop to 14.5V is due to 94% efficiency, i.e to 6% switching losses?
Is this an expected level or could we expect higher efficiency even?
B.r M.A.M

0 Robert Clifton56 over 6 years ago in reply to M.A.M

TI__Mastermind 27590 points

Hi M.A.M,

If they are running the device at maximum power then have they checked the voltage sag from their power supply? I've seen it before where the voltage at PVDD decreases during times when the amplifier is running at high powers. Please verify.

Best Regards,
Robert Clifton

0 M.A.M over 6 years ago in reply to Robert Clifton56

TI__Expert 8805 points

Robert, it is a TI EVM with bench supply. Not sure about internal resistance of that one. Will check.

B.r M.A.M

0 Robert Clifton56 over 6 years ago in reply to M.A.M

TI__Mastermind 27590 points

Hi M.A.M,

Even heavy duty bench power supplies can have a little sag in them. I do believe that this could account for some of the losses you are seeing.

Regards,
Robert Clifton

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TPA3221: Feedback on driving 2 ohm in BTL