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LM4871:Pop Up Noise Solution Inquiry

Park Kyungtae
Prodigy 60 points
Part Number: LM4871

Tool/software:

Hello, I have a question about the LM4871MMX/NOPB circuit.

The circuit is configured as shown in the attached image.

The problem is that Pop Up noise occurs when power is supplied.

In order to solve the Pop Up Noise, I lowered the audio amp input capacitor value from 390 -> 10nF and conducted a test.

The Pop Up Noise sound was confirmed to be reduced, but the overall volume of the amp also decreased.

I designed it based on the reference circuit in the datasheet, but it was not resolved.

The speaker uses CDS-4410-54SP of cui device, and the main specifications are as follows.

1. Impedance: 4 ohm
2. Max power: 6W

I would like to ask which part should be modified, so please reply.

  • 0
    TI__Guru** 102045 points

    Hi Park,

    The volume reduction in your application is most likely due to the cutoff frequency of the input high-pass filter being shifted too low by reducing the capacitor value. You can adjust the Ri value accordingly to keep a similar cutoff frequency, then use the same value for Rf to keep the gain as 1V/V.

    In general pop is related to capacitor charge/discharge and impedance matching, low tolerance passive components are good to consider. 1uF bypass capacitor is recommended, you may try with larger bypass cap and see if that helps also.

    Best regards,
    -Ivan Salazar
    Applications Engineer