TPA6132

Hi Eli,

How is your 3.5mm jack connected? Is the jack sleeve/ground connected to Digital GND as well?
As the headphone amplifiers are single-ended output class-AB amplifiers, each speaker needs a return path to ground, ideally it should return to the amplifier's ground. If this connection is not present there could be noise.
You can try with TPA6132A2 but there is a chance that the noise could still be present if the ground connection is not shared between the headphone speakers and the amplifier.

Best regards,
-Ivan Salazar
Texas Instruments

Hi Ivan,

We don't have 3.5mm jack connector in the glasses, to prove that the ground connection is the problem I cut the headphones wires (HSL, HSR, GNDHS) and connected them directly to a 3.5mm jack. 

In our application the micro USB connector is use as USB and as interface to headphones.

The micro USB is connected to the digital ground and therefor I connected the headphone ground feedback (GNDHS) to the digital ground.

Hi Eli,

The problem could be that the digital ground is too noisy. Or that there is not a proper way for the headphone ground to come back to the headphone driver. Analog signals in digital environments can be highly distorted.
Using the TPA6132A2 could improve the noise performance but as the connection to GND will be the same, the noise could still be present. Is there a chance that TPA6132A2 could be implemented after the USB connector? I mean, at the other side of the system; this could at least permit the headphone GND to connect directly to the headphone amplifier.
A possible workaround could be to provide a direct connection from GNDHS and headphone GND to the USB connector. Have you tried to place filters before the headphones to verify if there is any improvement?

Best regards,
-Ivan Salazar
Texas Instruments

I verified that the analog signal doesn’t have digital noises from digital signals nearby.

I place filters before the headphones and we didn't see any improvements and I also connect the GNDHS signal

directly to pin 5 in the micro USB connector (GND) without any improvements.

 

I don't understand how we can place the TPA6132A2 after the micro USB connector, could you clarify what you mean.

 

I don't have the TWL6040 headphone amplifier topology but I assume that the GNDHS is a virtual GND and not

a real analog ground that connected at one point to the digital ground and therefore I want to convert the audio

from virtual ground to signal that reference to the digital ground.

Hi Eli,

Now I understand your intention to use TPA6132A2. This could actually help to reference the signal to digital ground.

Best regards,
-Ivan Salazar
Texas Instruments

connected the TPA6132A2 eval board to my pcb and the noises level are acceptable.

The TPA6132A2 package is too big for us (3mm X 3mm) and I want to use TI TPA6136A2 that has smaller package (1.6mm X 1.6mm). 

Also the tow IC seems similar they has different recommendation on how to connect the SGND signal.

The TPA6132A2 diagram show that we can connect the SGND to the digital GND and the TPA6136A2 diagram shows that the SGND should be connected to the headphone.

 

Because we are using the micro USB connector also as our Audio connector we must connect the SGND to the digital GND.

Can we connect TPA6136A2 SGND signals to digital GND as I do in the TPA6132A2?

Hi Eli,

You can connect TPA6136A2 SGND the same way you do with TPA6132A2.

Best regards,
-Ivan Salazar
Texas Instruments