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LM4950: LM4950 burns when connected to a battery

Muhammad Faisal
Prodigy 120 points
Part Number: LM4950

Hi,

When I am using LM4950 audio amplifier with a 12V/2A adapter, it works completely fine, but when I connect to a 12V battery  (can source up to 20 A current) the amplifier burns. I tested it with two boards and got the same result. The DAC_SHUTDOWN pin is floating in the beginnig.  The output of the amplifier is connected to the transformer and no load is connected to the output of the transformer.

Any ideas?

Regards

  • 0
    TI__Guru* 95335 points
    Hi Muhammad,

    Have you captured the current consumption of the device from the 12V/2A adapter?
    Is there a chance that there is anything else different from one setup to another? Have you measured battery voltage just to see if there is a chance that voltage goes higher than specified?

    Best regards,
    -Ivan Salazar
    Audio Applications Engineer - Low Power Audio & Actuators
  • 0 in reply to Ivan Salazar
    Prodigy 120 points

    Hi,

    Yes, I checked the battery voltage before connecting. It was 11.5 V.  There is nothing different except the battery.

    It doesn't even get warm when connected to the adapter. I haven't measurement the current but I am pretty sure that it will be very less as no load is connected to the audio amplifier.

    I am really confused why it acts different with the battery. If there is no load then the audio amplifer should not draw huge currents. And as I said, I checked it with two and got the same result.

    Regards

  • 0 in reply to Muhammad Faisal
    TI__Guru* 95335 points

    Muhammad,

    Could you try with load connected and not using a transformer? Or at least not using a transformer?

    Best regards,
    -Ivan Salazar
    Audio Applications Engineer - Low Power Audio & Actuators

  • 0 in reply to Ivan Salazar
    Prodigy 120 points

    I tried with another 12V battery (8AA cells connected in series) and it worked fine. The battery I was using was Lipo battery but still not sure why two of my audio amplifiers burned.

    Anyways, I have another question. When I play an audio file (raised cosine chirp signal), the audio amplifiers generates some sound (like clicking). As I mentioned in the previous message that the output of the amplifier is connected to the transformer. I have checked the signal at the output of the transformer and it looks fine but not sure why the amplifier makes this sound. 

    Regards

  • 0 in reply to Muhammad Faisal
    TI__Guru* 95335 points
    Muhammad,

    This is most likely caused by the transformer load. Could you try by connecting the speaker directly to the amplifier outputs? (Remove the transformer) This is just to verify that this is due to the transformer.
    The following document covers some constraints when driving a transformer load:
    www.ti.com/.../sloa133.pdf

    Best regards,
    -ivan Salazar
    Applications Engineer - Low Power Audio & Actuators