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5V Reference to a PIC working in 3.3V

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UroBoros

UroBoros

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My PIC is working with 3.3Volts.
I am providing Vref+ and Vref- pins with reference levels.
ADC reference cannot be more than Vcc, that is what I understand.

So is it possible to Apply 5Volts between Vref pins to measure 5 volt span when working voltage is only 3.3V
 

Pot down the 5V input to within the 3.3V range.
 

Use a voltage divider where R1 is 10k and R2 is 4k7. When Vin is 5v, Vout will be 3.3v. Thus, you can program the ADC to show 5v when decode 1024 (10000000000).

Resistive_divider.png


Regards.
 
UroBoros said:
That is not the thing. Can the span be from 0to 5 by clamping Vref- to 0V and Vref+ to +5V?
Click to expand...

Did you not say "ADC reference cannot be more than Vcc, that is what I understand." so doesn't that by default mean you can't have Vref=+5V anyway? So what's the point of your "thing"?
 

You cannot exceed absolute maximum ratings. In general for most inputs the maximum allowed voltage is near VDD (VCC).
The pic datasheet is clear:

Absolute Maximum Ratings
Voltage on any combined analog and digital pin and MCLR, with respect to VSS ............... -0.3V to (VDD + 0.3V)
Voltage on any digital only pin with respect to VSS when VDD < 3.0V............................. -0.3V to (VDD + 0.3V)
Click to expand...

So you need to keep Vref and the input of the ADC to no more than 3.3v or even less to be sure.
 
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