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STM32L47x ADC maximum input voltage

Question asked by Vogel.Markus on Apr 26, 2017
Latest reply on May 9, 2017 by Vogel.Markus

Dear all,

I have the following situation:

  • STM32L471/L476 processor
  • Using the ADC with the internal reference buffer (2.5V) as analog eference
  • One of the ADC input signals comes from a rail-to-rail OP-AMP with 3V supply voltage, so this input signal can be up to 3V, and therefore higher than the ADC reference voltage
  • Normally this ADC input signal will be within 0 to 2.5V but it might occassionally exceed that range and then go up to 3V

 

Now my question is:

Is it a problem when the ADC input voltage is above the reference voltage? I know that some ADC's can get damaged in this case. In the datasheet I found that

  • GPIO VIN max = 4V (STM32L476xx Datasheet, DocID025976 Rev 3, Table 18)
    • This absolute maximum rating I would fulfill
  • ADC VAIN Conversion voltage range max = VREF+ (STM32L476xx Datasheet, DocID025976 Rev 3, Table 62)
    • This looks like it is just where the ADC converts but not like a do-not-exceed limit

 

So if the ADC in this configuration can get damaged by a 3V voltage I would look for some alternative (other reference, limit input signal externally) but it would be the best if it could withstand it.

 

Additional information:

  • I cannot use the 3V supply of the OP-AMPs as it is switched on/off but I need a constant analog refernce since I require the DACs all the time
  • Using another 3V supply would be possible but costly (this is a device prototype)

 

Hope you could undestand my problem, otherwise just let me know.

 

Thanks in advance and kind regards

 

Markus

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