• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 29 subscribers
  • Views 1008 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM4871: high frequency output

Dongbao Zhou
Expert 4000 points
Part Number: LM4871

Hello team,

My customer got a 3.4MHz 0.9Vp-p sinusoid waveform from pin8 to GND even no audio input, we can still see this high-frequency signal with audio input.

Could you help advise how to solve this issue?

Dongbao

  • 0
    TI__Guru** 102105 points
    Hi Dongbao,

    Perhaps this is a noise signal that is coupling into the device output. In that case you could add a ferrite bead filter at the output.
    One question: Why is there a cap between Vo1 and Vo2?

    Best regards,
    -Ivan Salazar
    Applications Engineer - Low power Audio & Actuators
  • 0 in reply to Ivan Salazar
    TI__Expert 4000 points
    Hi Ivan,

    Thanks for your reply.
    Customer test this device with clean 5V input, and other parts were not working during test. Another comment is we can see the signal from pin 4 to GND when C104 is removed. Any other comments regarding the possible root cause?
    I think the cap between Vo1 and Vo2 is used for filtering.

    Dongbao
  • 0 in reply to Dongbao Zhou
    TI__Guru** 102105 points
    Dongbao,

    Have you tried by removing C133? And perhaps also C135 and C136?
    I'll keep looking for possible root cause.

    Best regards,
    -Ivan Salazar
    Applications Engineer - Low power Audio & Actuators
  • 0 in reply to Ivan Salazar
    TI__Expert 4000 points
    HI Ivan，
    Thanks for your reply. We can solve this problem by reducing c135/6 from 2.2nF to 100pf, Could u let me know the reason? i didn't see very long route of the output.
    Dongbao
  • 0 in reply to Dongbao Zhou
    TI__Guru** 102105 points
    Dongbao,

    Capacitive loads could drive the Class-AB amplifiers into instability. Perhaps this is what is happening here.
    If C135 and C136 are needed they could try to add series resistors at the outputs (pins 5 and 8) to isolate the capacitance from the device outputs.

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