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Hot!AVDD current consumption

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jronne
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2008/12/02 17:36:45 (permalink)
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AVDD current consumption

I am working on a new design and I have searched everywhere trying to find a specification for the current consumption on the AVDD pin. I want to have this pin tied to a 5Vref instead of the 5V on VDD for higher accuracy, but I don't want to oversize it. Where is this spec? I would assume it changes based on samples per second, but I can't even find a max consumption. Where is this spec???
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    barum
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    RE: AVDD current consumption 2008/12/02 18:02:07 (permalink)
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    ORIGINAL: jronne
    Where is this spec???

    In device datasheet.

    As example, for dsPIC30F6014A, document DS70143C, page 210, TABLE 23-38: 12-BIT ADC MODULE SPECIFICATIONS,

    IREF,  Current Drain:
    typ. operating  150 μA, max 200 μA
    typ. off  0.001 μA, max 1 μA

    #2
    Kiwi Mike AZ
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    RE: AVDD current consumption 2008/12/02 18:48:52 (permalink)
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    What Part are you using.

    This is a power supply pin NOT a reference pin.

    You can add LC or RC filtering to this pin to improve noise level at this point.

    Note it powers more than just the analog section of the device... it powers some of the digital section and in a number of devices is powers the programming/debug section.

    The specs previously mentioned are for the reference - not for the AVdd pin

    Mike
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    jronne
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    RE: AVDD current consumption 2008/12/08 10:17:47 (permalink)
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    While it is a power supply pin, it can be used as the reference for the A/D. I am using the reference input pins as analog ins, and want to use this as my reference voltage (See figure 20-1 page 134 of the dspic30F4011_4012 manual for a pictorial) . I am well aware of filtering for noise and probably know more about this kind of thing than 99% of the people on this forum. I need to know the current consumption of the AVDD pin, not the reference pin.  I don't know why there seems to be no documentation for this.
    #4
    leon_heller
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    RE: AVDD current consumption 2008/12/08 11:37:05 (permalink)
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    The current taken by AVdd depends on how the chip is configured and what it is doing, like the other supply pins. I don't think I've ever seen it specified on any chip.

    Leon


    Leon Heller
    G1HSM

    #5
    jronne
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    RE: AVDD current consumption 2008/12/08 14:45:00 (permalink)
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    Well here is the answer I got from tech support:
    {/quote}
    To obtain this specification you would need to submit a NSCAR (Non-Standard Customer Action Request) to your local Microchip sales office at:
    http://www.microchip.com/sales

    In order to gain a rough approximation, consider that much of the current will come from the action of measuring.  Note that the load current can be fairly large, probably in the mA range when operating, due to the fact that a capacitor has to charge quickly.  Since its a small cap, it will be only a short current spike, so the avereage operating current should be quite low, but this would depend on how many conversions per second you do.  I'd suggest to get a better understanding of it, put a 1 ohm in series with AVss (and AVdd) and watch the results on a fast scope when doing a conversion.  With 1 ohm, you can easily see 1mA as 1mV, if you need more range, use a larger resistor, but obviously you can't go too far (say a few 100 mV) before the votlage drop will invalidate your experiment.
    {\quote}

    I was really hoping they could tell me something along the lines of: Assuming you are using 5V, and taking 1Msps spread over all Analog channels, the worst cast current into AVDD would be XmA.

    Well, I will hope it's not more than 5-10mA and if it is, I guess I'll have to fix it.
    #6
    rangel
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    Re: RE: AVDD current consumption 2016/07/07 13:35:11 (permalink)
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    Hi Jronne,
     
    I also have the same problem that you.
     
    You could determine the maximum current at pin Avdd ?
     
    I am using Dspic33ep512mc502.
     
    Thank's.
    #7
    NKurzman
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    Re: RE: AVDD current consumption 2016/07/07 13:59:45 (permalink)
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    In the End it is not a alternate Vref Pin.  You will not get The same performance from it as you would Vref.
    You would be better served Muxing some Analog pins, or getting a PIC with the needed number of pins.
     
    #8
    Javier Lopez
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    Re: RE: AVDD current consumption 2019/05/22 01:56:16 (permalink)
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    The spec is at ADCx module specifications, in my dspic33ep128 it said 5mA using 10bits adc and 2mA with 12 bits.
    I think with a 1uF MLCC cap and independent power supply or 1.5A regulator you should have enough accuracy :)
    #9
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