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Hot!PIC18F: minimum supply voltage for FVR using 4V reference

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dg123
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2020/02/07 16:46:18 (permalink)
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PIC18F: minimum supply voltage for FVR using 4V reference

On the pic18F46k22 I want to use the 4V reference, but I can't find what the minimum supply voltage spec is before starts to lose accuracy. The closest thing to a spec seems to be on page 445 of the datasheet where it suggests > 4.75V, but the reference seems to work reliably well below that number. Is 4.75V the minimum or will it be ok to go below that?
#1

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    acharnley
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    Re: PIC18F: minimum supply voltage for FVR using 4V reference 2020/02/07 17:00:19 (permalink)
    +1 (1)
    You've lost accuracy just by using it, it's something like +/- 4%. Do you really need it? 0.1% resistors cost very little, two of them and you can use the 2.048v with it's 2% accuracy and not have to worry about Vcc dropping.
    #2
    coffee critic
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    Re: PIC18F: minimum supply voltage for FVR using 4V reference 2020/02/13 10:41:16 (permalink)
    -1 (1)
    Is this question still open?

    n_*$
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    dg123
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    Re: PIC18F: minimum supply voltage for FVR using 4V reference 2020/02/13 11:31:06 (permalink)
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    I would like an answer, yea
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    Bob White
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    Re: PIC18F: minimum supply voltage for FVR using 4V reference 2020/02/13 12:37:14 (permalink)
    +1 (3)
    From Table 27-3 of the data sheet, the tolerance of the reference is only specified for Vdd >= 4.75 V.  If i were do such a design I would take Vdd = 4.75 V as a very hard limit if I wanted a guarantee.
     
    There is no guarantee when Vdd is less than this.   You don't know how the reference voltage will be behave if Vdd becomes less than this.  You seem to assume that there is a gradual degradation of the tolerance.  I see nothing that suggests that is a good assumption.  For all we know, the reference could stop working entirely at Vdd = 4.7999 V.


    #5
    coffee critic
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    Re: PIC18F: minimum supply voltage for FVR using 4V reference 2020/02/13 13:34:46 (permalink)
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    You will need to submit a support ticket to get the device performance outside of the data sheet limits. 

    n_*$
    #6
    mlp
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    Re: PIC18F: minimum supply voltage for FVR using 4V reference 2020/02/14 16:45:18 (permalink)
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    coffee critic
    You will need to submit a support ticket to get the device performance outside of the data sheet limits.

    And it's likely the response will be "Hahahahaha! Don't do that. If you do, we don't care."

    Mark (this opinion available for hire)
    #7
    ric
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    Re: PIC18F: minimum supply voltage for FVR using 4V reference 2020/02/14 16:59:29 (permalink)
    +2 (2)
    Bottom line, data sheet specs are deliberately conservative, because the device is designed to meet those specs over all temperature, voltage and production run variations.
    Of course you will find most devices perform better than the specs, but you cannot depend upon it unless you do your own full range testing over all expected conditions on every unit you make.
     

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    #8
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