LM48511: Damaged after a day long of use

Hi Andrew,

You may also want to check your load impedance during long stress test. LM48511 may be damaged due to overcurrent as well, if the load impedance is reduced due to heating or similar this could happen.

You can send me a connection invite to share your files internally, then we can use private messages or share email addresses to follow up.

Best regards,
-Ivan Salazar
Applications Engineer

Ivan,

Thanks for the quick response.  I have been reading more forum posts and see there have been issues from two posts.  

https://e2e.ti.com/support/audio-group/audio/f/audio-forum/642124/lm48511-failure-of-lm48511

https://e2e.ti.com/support/audio-group/audio/f/audio-forum/796858/lm48511-lm48511-output-lagging-and-suddenly-stopped-playing-speaker

I also see that the PV1 voltage is high (over 8V).  I am lowering the regulator voltage down to ~6V to see if we get more stability.  It seems that there are posts that elude that there are thermal associated issues.  I currently have no heatsinking on my prototype at the moment, but plan to do something to add to heatsink.  If you have any other insights it would be greatly appreciated.

Thanks.

Oh, I forgot to mention that I am using a volume adjustable headset that reads around 300Ohm - 1.2KOhms impedance.  I guess you are saying that the speakers could be getting warm from the high volume audio it is receiving and the impedance is lowering?  Since I'm well above the 4 and 8 ohm impedance, I think it would be irrelevant for my case?  

I should also add that I am reading this forum post and I did add a filter at the output, because we failed EMI testing.  Could this be the reason for the amplifier failure?  I assume that it is possible to add a low pass filter on the output because the forum talks about a TI application note that uses one on the output.  Perhaps my implementation is incorrect?  I'm wondering if my inductor is sized incorrectly or should I have used a RC filter instead?  The link to that forum and schematic screen capture are below:

https://e2e.ti.com/support/audio-group/audio/f/audio-forum/935908/lm48511-should-i-use-filters-on-the-output-of-a-filter-less-class-d-amp/3488705?tisearch=e2e-sitesearch&keymatch=LM48511#3488705

Hi Andrew,

I'm taking a look at your issue description and will be back with further comments by tomorrow before the end of the day.

Best regards,
-Ivan Salazar
Applications Engineer

Ok, thanks for your support

I am running the evaluation board now with the low pass filter on the output.  So far it is running for 1.5 hours with no issues.  I'm going to keep it running for the rest of the day and through the night and will monitor it periodically.

Thanks.

Hi Andrew,

I'm not clear on the output filter, are you trying now with the filter populated or not? And did you had it connected before?
Please let us know how the test goes.

From previous experience with this device, you need to be careful with transients and peaks at the output or it could get damaged. Q factor of the filter must be damped to make sure no ringing can affect the device outputs.

Your load impedance seems to be high enough to not care about impedance reduction after long play times.

Best regards,
-Ivan Salazar
Applications Engineer

Yes, I initially ran the eval board as is and it works just fine.  I then added the low pass filter and ran the test again and it is working fine.  So we are still at a loss as to the root cause of the issue.  So far the only theory is that the Audio Codec on the audio amplifier input might have produced a large spike causing the failure of the amplifier.  

We aren't planning to use the audio a lot except during failure alerting conditions.  We are still in the middle of development of hardware and software and will continue to monitor this.  I will let you know any additional information if this happens again.  We are getting are small batch of prototypes fixed now and will see if anymore are damaged during use.

Hi Andrew,

Understood, thanks for the notice. If you need further assistance please let us know, if this thread is still open you can reply back or you can always start a new thread.

Best regards,
-Ivan Salazar
Applications Engineer