TPA3110D2 Hiss Noise

Hi Kato-san,

Can you please describe the hiss noise in detail? What is the test conditions? Do they have the FFT plots to capture the noise? Are they able to duplicate the issue with EVM? Tried using a good bench power supply? How about the input audio grounding? What is the audio source?

reg,

Paul.

Hi Paul-san,

Thank you for your reply quickly.
Our customers are evaluating by using the test board that they designed.
They said that when they do not input audio signal, they heard a noise from a speaker.
Although they supplied it from the external stabilized power supply instead of the DCDC, the phenomenon did not change.
And the ground does not seem to have any problem.
We have not obtained schematics of it, are going to meet them at next week, evaluate it with them.
Could you please advise us about it?

Best Regards,
Kato

Hi Kato-san,

I would suggest to run the same test setup with EVM and see if the issue can be duplicated. Can they share the schematic of how the audio inputs are connected to the audio source? Single-ended input for diff input? Maybe they can describe it.

I would suggest take a look at the layout and make sure that there is no high frequency signals or power traces near the input traces of the amp. Are the inputs left floating without input audio signal?

reg,

Paul.

Hi Paul-san,

Thank you for your reply.
Unfortunately because we do not have the EVM for TPA3110D2, we can not begin to evaluate it quickly.
First, we will evaluate it with our customers.
The topology that they used is single-end input.
They connected a capacitor between dac output and positive input, connected a capacitor between the negative input and ground.
It is really a little more complicated schematics.
Although the positive input is left floating, the hiss noise occurred.
Moreover, when they increase the gain, the hiss noise also increased.
We believe that this cause is due to the inputs of the amplifier.
We will request schematics and board patterns around inputs of amplifier to our customers.

Best Regards,
Kato

Hi Paul-san,

The meeting with our customers became the rescheduling at next week.
If we obtained schematics and board patterns around inputs of amplifier, we will send your e-mail through private message.
Could you please check it?

Best Regards,
Kato

Hi, Geert,

Thanks for your comments! It's always good to hear our customer's perspective - sometimes we kind of have "blinders" on and it's good to get more insight!

-d2

Hi Geert-san,

Thank you for your reply.
We will talk our customers this issue while considering your opinion.

Best Regards,
Kato

Everyone,

This was a matter for our customer's design.
We could solve the hiss noise.
Thank you for your advice.

Best Regards,
Kato

Hi, please see attached schematic and layout. Since building the PCB, I've ensured that signal ground and amp ground are connected together. Single ended input. Left and Right negatives are connected to ground via the 3.3u capacitor. I realised that the left and right signal routing were crossed over and this has been removed and a direct wire link connected between the 3.5mm pins to the respective L+ and R+ decoup capacitors. Thank you.

Hi Shawn. I seem to have fixed the problem. I was concerned the noise was coupling into the differential inputs, so i used a couple of signal transformers to convert the single ended inputs to differential. Pin drop silence now :).