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PGA2310: Looking for a digipot that can be used in a floating configuration

Part Number: PGA2310
Other Parts Discussed in Thread: PGA2320

I've been looking for a digipot to use in my amplifier for the volume control etc.

The issue I have though is I need the pot to be floating, which it doesn't appear is possible with this device.  Can someone confirm this, and if that is the case, is there an alternative device that can be used?

Regards

Tom Simmons

  • Hi Tom,
    What do you mean by "floating" in this case? Do you need the PGA analog ground to be separate from its digital ground? If this is the case, it may be possible to use a digital isolator and tie the PGA grounds together locally, while keeping the overall digital and analog grounds separate.
  • Alexander

    The mechanical potentiometer (10K lin) currently in use has neither end grounded.  Whilst it is a volume control, it is in the feedback of an op-amp so that it can be made to give a log response to the pre-amp.

    Tom

  • Hi Tom,
    I think PGA2310 would be best used as a replacement for a baxandall-style volume control, as it already gives a logarithmic adjustment of volume. Alternatively, it looks like TPL0501 is a digipot which supports 3-terminal applications.
  • Alex

    Unfortunately the TP0501 isn't the correct resistance, is only single channel and doesn't appear to have the zero crossing detection which would result in the "zipper" noise effect when changing volume.


    Tom
  • Hi Tom,
    I'd suggest using the PGA2310 in place of your volume control circuit. It will provide the zero-crossing detection and log response you are looking for.
  • Alex

    The PGA2310 is where this all starter, I wanted to know whether it could be used in a fully floating configuration.

    Tom

  • Tom,

    The PGA2310 is a digital pot followed by an op-amp buffer (and that buffer has variable gain when the gain is above unity), so it cannot be floated as you wish.

    If the goal is to replace the mechanical pot in an existing circuit, then the PGA2310 won't work. There are plenty of digital pots from some of TI and their competitors which would work, but be mindful that for example the TPL0501 has a limited voltage range and digital pots that can handle ±15 V rails are pricey, and log taper is harder to find. (You could probably slug the pot with a fixed resistor to approximate log taper; the question is does absolute gain matter?)

    But if the project is not already completed and you have the option, I agree with Alex Davis: replace the output volume control circuit with the PGA2310 (or PGA2320) and be done with it. The parts work as advertised. Make sure to drive the PGA2310's analog inputs with a low-impedance source.