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LM4808 click suppression / non-inverting configuration

Jonathan9420
Expert 2056 points
Other Parts Discussed in Thread: LM4808, TPA6132A2, TPA6130A2, TPA6133A2, LM4810

LM4808 datasheet says "Switch On/Off Click Suppression" and then talks about capacitor values that raise the bias voltage slowly.  Is there actually a suppression circuit in the IC, like a mute circuit when the positive input is lower than some threshold?  Or is it just behaving like any other op-amp and it's a matter of making the positive input rise slowly and AC coupling the input so the output also rises slowly?

We've been using it in non-inverting configuration, which seems to work fine, but when the power is turned on, it pops very loudly, and maybe non-inverting configuration is not recommended for other reasons, too?

  • 0
    TI__Guru**** 189399 points

    Hi, Jonathan,

    If you're after awesome performance (including pop), I suggest that you check out one of our newer amps like TPA6132A2, TPA6133A2, or TPA6130A2.

    We usually don't disclosure our internal design techniques, but you are correct, good pop performance is a combination of our circuit used with the correct external components.

    -d2

  • 0 in reply to Don Dapkus
    Expert 2056 points

    Don Dapkus said:
    If you're after awesome performance (including pop), I suggest that you check out one of our newer amps like TPA6132A2, TPA6133A2, or TPA6130A2.

    Those are significantly more expensive, though.

    I just found the LM4810 datasheet, which also claims "click and pop reduction", and describes how it works:

    During turn-on, the LM4810's internal amplifiers are configured as unity gain buffers. An internal current source charges up the capacitor on the BYPASS pin in a controlled, linear manner. The gain of the internal amplifiers remains unity until the voltage on the BYPASS pin reaches 1/2 V DD . As soon as the voltage on the BYPASS pin is stable, the device becomes fully operational.

    Does the LM4808 work the same way?

    The example circuit for the LM4808 has VDD connected to both the amplifier and the bias resistors.  If the bias resistors and capacitor are powered up and then the amplifier is powered up after it's reached VDD/2, I suspect it will still pop?  So if we are switching the power to the amplifier, it also has to be switched to the bias resistors at the same time?

  • 0 in reply to Jonathan9420
    TI__Guru**** 189399 points

    Hi, Jonathan,

    Yes, you will want to power the bias and VDD from the same supply to minimize pop.

    -d2