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LM4675: L4675 failures - IC Class D Audio Power Amplifier - No Sound Output

Julius Punzalan
Prodigy 20 points
Part Number: LM4675
Other Parts Discussed in Thread: TPA2011D1, TPA2039D1,

Hi TI,

 

I would like to get some expert feedback regarding recent failures of amplifier chip L4675 on our customer’s boards. There was no audio output and

replacing the amplifier chip itself fixes the problem. Our challenge currently is that the board assemblies are not tested not until they reach our customer.

 

We’ve done quite a bit of investigation ourselves including verifying the solder reflow process and PCB design and we believe it is not related to either.

Most of the boards we received did not have any solder bridge for the chip. We have received the batch of ICs last Sep 2016 and the date code is 1549 and the rest in our inventory were already quarantined, planning to be sent back to Ti for failure analysis.

 

When we remove the chips, it was found that there is electrical short either between pin 5 to 6 and/or pin 8 to 6 meaning the output side is busted.

Any advise why could this happen? If the speaker is connected while the board is already powered up, will this cause the chip to blow up internally?

I think if a certain defective speaker (shorted) was connected, it will also bust out the output side of the chip.

 

regards,

Julius Punzalan

Any feedback is most welcome. We are not convinced this is date code related but we are still sending for FA for investigation purposes.

  • 0
    TI__Mastermind 20085 points
    Hello Julius,

    Welcome to E2E, thanks for your interest in our products.
    Could you provide me more details when the problem happens? and, could you provide me a schematic and a PCB layout? In order to review everything is right.
    To connect or disconnect the speaker shouldn't cause damage. Did you make this test with different speakers?

    Best Regards
    José Luis Figueroa
    Applications Engineer
  • 0 in reply to José Luis
    Prodigy 20 points

    Hi Jose,

    Thanks for taking time to look into this. I don't have a schematic right now. Our customer is the one testing the boards and plugging the speaker.

    I was thinking more now that a 'defective' speaker could cause damage to the chip. There's been a reasonable number of failed boards and I am suspecting that a 'defective' speaker

    made its way back to the good batch of speakers and eventually getting picked again and plugged into another new untested board, thereby busting the amplifier chip. This could be the reason why failures

    have been piling up.

    I saw somewhere in a thread here that you replied to a certain inquiry and you've confirmed that this chip doesn't really have short circuit protection. So, if there is a short-circuited load like a defective speaker,

     the chip could get damaged. Looking at the PCB layout and parts, I can only see an ESD bipolar diode protection from the output lines to the ground. Anything we could do to prevent this from

    happening? Thanks.

    regards,

    Julius Punzalan

  • 0 in reply to Julius Punzalan
    TI__Mastermind 20085 points
    Julius,

    First of all, this device just has thermal protection. Second of all, you should review if the problem is caused by defective speakers.
    Finally, if the defective speakers are the problem and the device is using the DSBGA package, so I could have a look at the following devices TPA2011D1 and TPA2039D1. They are Class-D audio amplifiers with have auto-recovering short-circuit protection and they are cheaper than LM4675.

    Best Regards
    José Luis Figueroa
    Audio applications Engineer