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PGA2311 power supply

Radim Beran
Prodigy 20 points
Other Parts Discussed in Thread: PGA2311

In my project  I'm using separate power supply for digital part (+5V)  and for analog part (+/- 12V  and +/-  5V V for VA+ and VA- PGA2311 ).  The digital PS is still active also supplying VD+ of PGA2311 while analog is activated only when my device is turned on. When is device turned off, PGA is in supply mode VD+=5V, VA+=0V, VA-=0V. I found that the current of PGA in this mode is higher and PGA is little hot. AGND and DGND are unjoined. 

I must say that my preamplifier works good and sound is perfect, but:

  • Can I use PGA2311 in this mode VD+=5V, VA+=0, VA-=0?  Or could I better apply VD+ from VA+ via small resistor?
  • Can I leave AGND and DGND unjoined? 

Thank you for your answer.

  • 0
    TI__Mastermind 27715 points

    Hello Radim,

    It's no problem to only apply VD+ to the PGA2311 for a brief amount of time, but only the digital circuitry will be active. The analog signal path will be held in a MUTE state until the analog power supplies turn on. The absolute maximum table specifies that the difference between VA+ and VD+ should be less than or equal to ±300mV.

    However, you cannot leave AGND and DGND disconnected from each other. The separate pins are provided such that separate analog and digital ground planes can be used, preventing switching digital signals from coupling into the analog signal path. However, these nodes must be connected together at one point - see Figure 6 in the PGA2311 data sheet.

    Leaving these pins disconnected from each other is most likely the reason for the extra current consumption when only VD+ is applied, since the analog circuitry is floating and strange bias conditions can develop inside the PGA.

    Best regards,

    Ian Williams
    Linear Applications Engineer
    Precision Analog - Op Amps 

  • 0
    Prodigy 20 points

    Hello Ian,

    thank you very much for your answer to my question. I applied your advice and now is everything OK.

    Radim

  • 0 in reply to Radim Beran
    TI__Mastermind 27715 points

    Great! Glad to hear that everything is working properly.

    Best regards,

    Ian Williams

  • 0 in reply to Ian Williams
    Prodigy 20 points
    Hi Ian,

    My pre-amp project is similar to Radim in which I'm using separated 2 sets of power transformers and rectifiers to supply separated +5V for digital circuit and +/-5V for analogy circuit.

    In order to separate the digital and analogy parts ideally, the AGND and DGND are not connected. The pre-amp seems work fine up to now. Would that cause any damage and problem to the PGA2311 chip in short and long term?

    For my case of totally separated power supplies, if the AGND and DGND must be connected, will any problem would be caused?

    Thank you so much.
    Eric
  • 0 in reply to Eric Man
    TI__Mastermind 27715 points

    Hello Eric,

    I cannot speculate as to the long term effects of operating the PGA2311 with AGND and DGND disconnected. The data sheet specifies that these nodes must be connected, so if you do not follow this requirement you do so at your own risk.

    It's possible to keep the ground planes separate, in order to keep the analog and digital signals return currents separate, but even so these planes should be connected at least at one point as shown in Figure 15 of the PGA2311 data sheet. If not, unknown bias conditions inside the PGA2311 could develop if the ground voltages move apart.

    Best regards,

    Ian Williams

  • 0 in reply to Ian Williams
    Prodigy 20 points

    Hi Ian,

    Thank you for your prompt reply and suggestions.

    On the other hand, for the ZCEN(pin 1), if I always want to enable zero crossing function, do I need to add a pull-up resistor(e.g. 10k) in order to set it in active HIGH? Or simply apply +5V to pin 1 from VDD+ ?

    Best Regards,

    Eric

  • 0 in reply to Eric Man
    TI__Mastermind 27715 points

    Hello Eric,

    Either implementation will work, however I recommend using a pull-up resistor. This will limit the current into the device in case of any large transient voltages on the power supply.

    Best regards,

    Ian Williams

  • 0 in reply to Ian Williams
    Prodigy 10 points
    Hello Ian,

    I am also using a PGA2311 in my design.
    It appeared that some broke unexpectedly, with no output signal, and hot chip (with more that 100mA drawn on one analog power supply instead of the usual 10mA).

    Apparently, having 5V on VD+ and nothing on VA+/VA- is no problem according to your answer above.
    But what if I apply VA+ and VA- power supply, with no power on VD+ ?

    I feel concerned about the "< 0,3V" between VA+ and VD+ indication in the Absolute Maximum Ratings.
    Something strange also, about the Minimum Digital High output voltage :
    (VA+) -1 for PGA2311U
    (VD+)-1 for PGA2311UA
    Is this a typo?

    Thanks for your help.

    Raphaël
  • 0 in reply to Quentin Houdayer
    TI__Mastermind 27715 points

    Hello Raphaël,

    While the part can handle the digital supply being active with no analog supply for a brief amount of time, it is not recommended to leave the part in this state for any extended amount of time. You are correct that the absolute maximum specifies that the difference between VA+ and VD+ should not be more than ±300mV. I would not advise applying VA+ and VA- without VD+.

    I agree that the way the high-level digital output voltage spec is given is strange. While VA+ and VD+ should be essentially the same voltage, I consider the minimum to be based on the digital supply, or (VD+) -1V.

    Best regards,

    Ian Williams