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Hot!DSPIC33EV256GM104 ADC reference monitoring

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RonGer
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2019/09/25 02:30:21 (permalink)
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DSPIC33EV256GM104 ADC reference monitoring

Dear all,
 
I'm looking for a way to monitor the reference voltage of the ADC. This means I also want to recognize shifts on the ground line.
For the PIC16 this is easy with the FVR, but the DSPIC33 seems to have nothing similiar.
I had the idea to measure AVDD and AVSS, but as I can see, I have to spent two ADC channels for doing that (and I'm actually not sure whether this makes sense). Is there any way to measure the AVDD and AVSS voltage internally or getting a information about the ADC reference voltage?
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    du00000001
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    Re: DSPIC33EV256GM104 ADC reference monitoring 2019/09/25 04:49:22 (permalink)
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    You're giving too little details:
    • Your ADC references are NOT AVDD resp. AVGND ?
    • If not: what then ?
    You could use the 7-Bit DAC to provide a signal to one analog input. Or use some external reference diode. There's quite a number of possibilities, but it really depends on your basic configuration and further details...

    PEBKAC / EBKAC / POBCAK / PICNIC (eventually see en.wikipedia.org)
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    RonGer
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    Re: DSPIC33EV256GM104 ADC reference monitoring 2019/09/25 04:58:02 (permalink)
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    My ADC reference is AVDD and AVGND (AVSS).
     
    I'm just looking for something that is similiar to the FVR of the PIC16.
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    du00000001
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    Re: DSPIC33EV256GM104 ADC reference monitoring 2019/09/25 05:16:31 (permalink)
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    As far as I remember, there's no easily accessible reference voltage in the EVs.
    But you are free to connect one (e.g. a TL431) externally to one of the ADC inputs.
    Or - provided the "accuracy" is considered sufficient - tap the Vcap voltage (a nominal 1.8 V - not sure about the precision).

    PEBKAC / EBKAC / POBCAK / PICNIC (eventually see en.wikipedia.org)
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    RonGer
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    Re: DSPIC33EV256GM104 ADC reference monitoring 2019/10/25 05:04:51 (permalink)
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    Hello,
     
    thanks for your reply. But how can I ensure that the ADC reference voltage is still in range. What is the concept for this controller? Monitoring the VCC?
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    du00000001
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    Re: DSPIC33EV256GM104 ADC reference monitoring 2019/10/25 07:15:49 (permalink)
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    The concept? Measure the output of an external low-voltage voltage reference:
    • When the external voltage seems to increase, in fact VCC is decreasing.
    • When the external voltage seems to decrease, VCC is increasing.
    So you'll have a setpoint (with a bit of tolerance) for the readings of the external reference.
    Deviations from this setpoint can be translated to deviations of VCC - in the opposite direction.
    (No - you can't monitor VCC directly if VREF is just a (maybe filtered) derivative of VCC. That's not possible.)

    PEBKAC / EBKAC / POBCAK / PICNIC (eventually see en.wikipedia.org)
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