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TAS5424A: Burned Loudspeakers

Steve Scarlata
Prodigy 170 points

Part Number: TAS5424A

We produce a product using 2 of the TAS5424 power amplifiers.  We have several thousand in service.  On 2 or 3 occasions we have had a return where all 4 of the speakers attached to one of the power amps ICs were burnt in the voice coils.  We inspected and tested the amplifier that was returned with these speakers and could not find any issues.  No DC offset or other malfunction.

The customer reported a very loud hissing/squealing sound which persisted for a while and resulted in a burning smell at the speakers.   We tried to reproduce the issue by pumping every imaginable signal through the amplifier,  full scale sine or square waves of every frequency for hours.  The speakers would get hot but never came close to the damage of the returned units.  Also tried various shorts across the amp output during operation or startup and it always triggered the protection as specified.

The only way to burn the speakers was to apply 21V DC directly across the speaker (The TAS5424A has a 21V supply in our design).  Then they burned similarly to the returns.

Has there been any history or observed cases where the TAS5424 could enter some failure mode or instability that could result in a largely DC output?  Any other reported cases similar from the customer base?

Thanks.

  • 0
    TI__Mastermind 45085 points

    Hi Steve,

    I am sorry to hear that you have this issue.  This seems to be a system issue, but I will try to direct you to a potential cause.

    The TAS5424A is a DC amplifier.  The only way we can get DC on the output is to inject DC into the input.  This can be caused by leakage in the coupling capacitor, but would need to be on all four channels.  It can also be caused by a conductive foreign particle on an input pin that caused a short to ground.  The foreign particle would be gone after desoldering.  These amplifiers are very stable and do not oscillate.  The amplifier could have oscillated, but it is highly improbable.  Are you using the DC offset protection in the device?  This would not allow DC offset to occur long enough to damage the speakers.