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TAS5414A - DC across the outputs?

Craig Buckley
Prodigy 20 points
Other Parts Discussed in Thread: TAS5414A

Hello TI

I has a  PCB designed with 2x TAS5414A amplifier devices that is the same schematic as the EVM.  Although I can measure a clean signal output across each of the amplifier terminals (post LPF), there is a large DC component that would destroy a speaker if connected without a DC blocking capacitor.  I have tried the DC reduction register settings and can see a 200-300mV reduction but the total DC right now is up to 2.5V with no load.

One of the chips is a straight 4-CH output while the other is configured in the PBTL for a total of 2-CH from the 4.  The PBTL channels have an average of 900mV DC while the standard configuration has a range of 850mV to 2.5V DC depending on whether or not a signal is present (with or without load makes little difference).  The positive output terminal has 5.7 to 7.3V DC while the negative output terminal has 4.8 to 6.4V DC across the various channels with and without signal present and they are never the same across the +/- terminals

You can draw huge currents from this DC component and I have now idea how to remove it.  The DC is there with or without a signal present but is highest with a signal.  Shorting the outputs with no signal trips the bench PSU.

With no signal the PWM is 53% on positive out and 47% on negative out at 407 kHz.  The DC supply is 12.5V

There are 2 basic things an amplifier should never do with one being DC on the output and the other oscillation.

Please help.

  • 0
    TI__Mastermind 37225 points

    Hi Craig,

    These small variations in DC offset at the output are probably not the device, but the system.  Please check the DC offset at the input pins.  Measure between the IN_P pins and in the IN_M pins.  There should be no DC measured.  Any DC at this point is amplified by the TAS5414A device.  If you measure DC at the inputs, it can be from leaky coupling caps on the IN_P and IN_M pins.  Another system issue that we found is that solder flux was not cleaned enough on the input pins and there is a some leakage current causing the DC offset on the inputs.

  • 0 in reply to Gregg Scott
    Prodigy 20 points

    Thanks Gregg

     

    You were right in that the input capacitors are a problem allowing some small DC leakage.  I was using affordable tantalum capacitors from a reputable brand.  I wonder if the leakage requirements should be included in the datasheet to avoid others finding out this issue or some note about the capacitor coupling concerns.  I noticed the EVM is using film caps which can be a bit pricey.  I substituted ceramic caps in a pinch to test and it all is good now with less than 20mV DC on all outputs.

    Thanks again

    Craig