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LM4950: Question

GARETH OU
Mastermind 8765 points
Part Number: LM4950

Hi

My customer has a question,
Vout(rms) is currently about 4V(rms)
RL=8 Ohm
The Input Level measured by Net VOUTL_OUT (C869) is about 0.38 (Vrms),

When Vout(rms) is adjusted to 5V(rms), the Vout waveform will begin to distort, please refer to waveform one and two,
The calculated output power is about 3~3.5W,
According to the LM4950 SPEC is still in the normal use specification, what causes the waveform distortion?
Please help clarify, thank you!

wave1

wave2

PROTEGO_A04_Audio AMP.pdf

  • 0
    TI__Guru* 95035 points

    Hi Gareth,

    Perhaps capacitors on the feedback loop could affect the response. These capacitors are mentioned only for piezo transducer applications, based on your speaker spec of 8 Ohm I don't think you're using piezo transducer.

    Could you try removing C54/C55/C69/C70?

    In addition, why is bypass pin connected to some additional circuitry other than decoupling capacitor? This is an internal reference path for decoupling only.

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

  • 0 in reply to Ivan Salazar
    Mastermind 8765 points

    Hi Ivan

    Customers remove C54/C55/C69/C70, there is no difference in the waveform before and after the removal, Do you have any suggestions regarding the distortion of the waveform? What waveform need to be measured?

    Thanks you

  • 0 in reply to GARETH OU
    TI__Guru* 95035 points

    Gareth,

    Do you have any feedback about the bypass capacitor?

    In addition, can you inspect the supply on VDD pin during your test? Also is there any difference if the speaker load is disconnected?
    There seem to be series capacitors at the outputs, Is there a difference on the measurements if scope is before or after these capacitors?

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