TPA3136D2EVM: Inductor value/testbench

Priya Nadathur70

Expert 2795 points

Part Number: TPA3136D2EVM
Other Parts Discussed in Thread: TPA3136D2

Hi,

From my recent thread about the audio demo,

While some switching noise is acceptable on one end of the resistive load, I'm seeing nearly

1 V p-p switching noise on the output waveform. Ideally, this should not be more than 250 mV p-p.

This is a problem, that may likely only be test bench related. A loudspeaker load (no LC filter) sounds

raspy, indicating that the differential output still has noise in it. I will be checking once more with

a new loudspeaker. In the product, this loudspeaker cable length can be as long as 4.5 feet.

I will take any new pointers for the testbench.

The LC filter I was using with the resistive load broke an inductor leg. Can I have a through hole

part number for inductor L1 from page 17, Figure 19 of the TPA3136D2 datasheet?

Thanks,

Priya

The inductor in the LC filter broke.

over 6 years ago

0 Shawn Zheng over 6 years ago

TI__Mastermind 24835 points

Hi Priya,
We are looking into this and will get back to you later.

0 Shawn Zheng over 6 years ago in reply to Shawn Zheng

TI__Mastermind 24835 points

Hi Priya,
Could you let me know your LC filter configuration(how much is the inductor value and capacitor value)? When you measure the noise on the output signal, please do it in differential mode by scope. If you can measure it with AP instrument, it's even better.
How is the external LC filter board connected to EVM board? Please make sure the connection/GNDing between them is good to achieve good signal integration performance.
Best ragards,
Shawn Zheng

0 Priya Nadathur70 over 6 years ago in reply to Shawn Zheng

Expert 2795 points

The LC filter values are the same from Fig 19 of the TPA3136D2 datasheet, C = 0.68 uF;

L = 10 uH. When I search for an inductor part, I see impedance ratings at different frequencies.

Is there such a rating you can share about this inductor so it can be replaced?

I will ask to see if an AP instrument can be rented. This a new thing at work.

I am pretty sure the LC filter is connected properly and grounded. It needed to be attached

and dismantled to the EVM many times, and it likely wore out. Picture attached.

Edited to add: I was able to find this part: SRF0905-100Y. 200 Ohm at 20 MHz; 10 uH at 1 kHz.

It is a SMT part. Please comment if this will not work and suggest a replacement.

0 kai klaas69 over 6 years ago in reply to Priya Nadathur70

Guru 140200 points

Hi Priya,

figure 19 shows a PBTL into 4R. This would mean 20W at a 4R load, resulting in a current of 2.2A. So, I guess the current rating of "SRF0905-100Y" is insufficient.

Kai

0 Priya Nadathur70 over 6 years ago in reply to kai klaas69

Expert 2795 points

Kai,
Thank you for your reply. The load is 4 Ohm 3W. Does this mean max load current is 0.866 mA? What should the inductor be rated for?
For a resistive load, I'm using two 8 ohm resistors in parallel, each rated at 3W.
Best Regards,
Priya

0 kai klaas69 over 6 years ago in reply to Priya Nadathur70

Guru 140200 points

Hi Priya,

yes, then the maximum load current would be 0.866A. Then a 1.6A rating should be ok. I any case, I would dimension the choke for the maximum possible current, to avoid overheating and burning... :-)

Kai

0 Shawn Zheng over 6 years ago in reply to kai klaas69

TI__Mastermind 24835 points

Hi Priya,
I found that you are using a line filter used for EMI suppression for the outpu filter. Could you please use a regular power inductors? You has a lot of candidates from Murata or WE.

0 Priya Nadathur70 over 6 years ago in reply to Shawn Zheng

Expert 2795 points

Can you give me a part number for the inductor? I will search for one now.
This maybe why I don't see a switching waveform when the filter is hooked,
otherwise I can.
Thanks,
Priya

0 Shawn Zheng over 6 years ago in reply to Priya Nadathur70

TI__Mastermind 24835 points

We have ever used 931BS-100M for the output filter. But you can find some inductors with a little lower rated current.

0 kai klaas69 over 6 years ago in reply to Priya Nadathur70

Guru 140200 points

Hi Priya,

it's the idea of the filter to make the switching waveform disappear behind the filter...

A "regular power inductor" is just a choke with low series resistance. Search for a choke with a rated current of 3A.

Kai

0 Priya Nadathur70 over 6 years ago in reply to Priya Nadathur70

Expert 2795 points

www.digikey.com/.../774878
Will this inductor work?
Thanks,
Priya

0 Priya Nadathur70 over 6 years ago in reply to Priya Nadathur70

Expert 2795 points

Used an existing inductor from an old board. There may have been wear and tear on the old LC filter. The new one soldered is sturdier. I eliminated use of any test point grounds on the EVM. I think this removed a lot of the switching noise from the single ended output.

Thanks,

Priya

0 kai klaas69 over 6 years ago in reply to Priya Nadathur70

Guru 140200 points

Hi Priya,

looks good now!

Kai

Audio

Audio forum

TPA3136D2EVM: Inductor value/testbench