AREF above operating voltage of the microcontroller












4














I’m operating an ATMega32 at 3v3 through USB and a LDO.



Is it possible to connect the AREF pin directly to the USB voltage of 5V so that I can read voltages between 0 and 5V when reading from the analog pins?






arduino avr







share|improve this question


















  • 4




    What does the datasheet say?
    – Elliot Alderson
    2 days ago










  • The microcontroller definitey can operate at 5V same applies to AREF it can operate under 5V, it is unclear to me if it can have a higher voltage than the one being fed through the VCC pins.
    – Petru-Sebastian Toader
    2 days ago








  • 3




    Indeed this information will be in the datasheet, but since it might be difficult to find I'll help a bit: The datasheet will state that the voltages at the uC's inputs/outputs cannot exceed the voltage on the VDD pins. The reason for this is the ESD protection diodes. As soon as the voltage at AREF becomes higher than VDD + 0.5 V the AREF's ESD diode will start conducting. If you want a 5 V input range either power the uC with 5 V or use a voltage divider to lower the input voltage to the ADC.
    – Bimpelrekkie
    2 days ago












  • Thank you! I’ll use a voltage divider as it’s the best solution in my case.
    – Petru-Sebastian Toader
    2 days ago






  • 2




    To learn more about what issues the ESD diodes can cause, watch this EEVBlog video: youtube.com/watch?v=2yFh7Vv0Paw Making this and comment above an answer because, well it is.
    – Bimpelrekkie
    2 days ago


















4














I’m operating an ATMega32 at 3v3 through USB and a LDO.



Is it possible to connect the AREF pin directly to the USB voltage of 5V so that I can read voltages between 0 and 5V when reading from the analog pins?






arduino avr







share|improve this question


















  • 4




    What does the datasheet say?
    – Elliot Alderson
    2 days ago










  • The microcontroller definitey can operate at 5V same applies to AREF it can operate under 5V, it is unclear to me if it can have a higher voltage than the one being fed through the VCC pins.
    – Petru-Sebastian Toader
    2 days ago








  • 3




    Indeed this information will be in the datasheet, but since it might be difficult to find I'll help a bit: The datasheet will state that the voltages at the uC's inputs/outputs cannot exceed the voltage on the VDD pins. The reason for this is the ESD protection diodes. As soon as the voltage at AREF becomes higher than VDD + 0.5 V the AREF's ESD diode will start conducting. If you want a 5 V input range either power the uC with 5 V or use a voltage divider to lower the input voltage to the ADC.
    – Bimpelrekkie
    2 days ago












  • Thank you! I’ll use a voltage divider as it’s the best solution in my case.
    – Petru-Sebastian Toader
    2 days ago






  • 2




    To learn more about what issues the ESD diodes can cause, watch this EEVBlog video: youtube.com/watch?v=2yFh7Vv0Paw Making this and comment above an answer because, well it is.
    – Bimpelrekkie
    2 days ago
















4












4








4







I’m operating an ATMega32 at 3v3 through USB and a LDO.



Is it possible to connect the AREF pin directly to the USB voltage of 5V so that I can read voltages between 0 and 5V when reading from the analog pins?






arduino avr







share|improve this question













I’m operating an ATMega32 at 3v3 through USB and a LDO.



Is it possible to connect the AREF pin directly to the USB voltage of 5V so that I can read voltages between 0 and 5V when reading from the analog pins?






arduino avr




arduino avr






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked 2 days ago









Petru-Sebastian ToaderPetru-Sebastian Toader

957




957








  • 4




    What does the datasheet say?
    – Elliot Alderson
    2 days ago










  • The microcontroller definitey can operate at 5V same applies to AREF it can operate under 5V, it is unclear to me if it can have a higher voltage than the one being fed through the VCC pins.
    – Petru-Sebastian Toader
    2 days ago








  • 3




    Indeed this information will be in the datasheet, but since it might be difficult to find I'll help a bit: The datasheet will state that the voltages at the uC's inputs/outputs cannot exceed the voltage on the VDD pins. The reason for this is the ESD protection diodes. As soon as the voltage at AREF becomes higher than VDD + 0.5 V the AREF's ESD diode will start conducting. If you want a 5 V input range either power the uC with 5 V or use a voltage divider to lower the input voltage to the ADC.
    – Bimpelrekkie
    2 days ago












  • Thank you! I’ll use a voltage divider as it’s the best solution in my case.
    – Petru-Sebastian Toader
    2 days ago






  • 2




    To learn more about what issues the ESD diodes can cause, watch this EEVBlog video: youtube.com/watch?v=2yFh7Vv0Paw Making this and comment above an answer because, well it is.
    – Bimpelrekkie
    2 days ago
















  • 4




    What does the datasheet say?
    – Elliot Alderson
    2 days ago










  • The microcontroller definitey can operate at 5V same applies to AREF it can operate under 5V, it is unclear to me if it can have a higher voltage than the one being fed through the VCC pins.
    – Petru-Sebastian Toader
    2 days ago








  • 3




    Indeed this information will be in the datasheet, but since it might be difficult to find I'll help a bit: The datasheet will state that the voltages at the uC's inputs/outputs cannot exceed the voltage on the VDD pins. The reason for this is the ESD protection diodes. As soon as the voltage at AREF becomes higher than VDD + 0.5 V the AREF's ESD diode will start conducting. If you want a 5 V input range either power the uC with 5 V or use a voltage divider to lower the input voltage to the ADC.
    – Bimpelrekkie
    2 days ago












  • Thank you! I’ll use a voltage divider as it’s the best solution in my case.
    – Petru-Sebastian Toader
    2 days ago






  • 2




    To learn more about what issues the ESD diodes can cause, watch this EEVBlog video: youtube.com/watch?v=2yFh7Vv0Paw Making this and comment above an answer because, well it is.
    – Bimpelrekkie
    2 days ago










4




4




What does the datasheet say?
– Elliot Alderson
2 days ago




What does the datasheet say?
– Elliot Alderson
2 days ago












The microcontroller definitey can operate at 5V same applies to AREF it can operate under 5V, it is unclear to me if it can have a higher voltage than the one being fed through the VCC pins.
– Petru-Sebastian Toader
2 days ago






The microcontroller definitey can operate at 5V same applies to AREF it can operate under 5V, it is unclear to me if it can have a higher voltage than the one being fed through the VCC pins.
– Petru-Sebastian Toader
2 days ago






3




3




Indeed this information will be in the datasheet, but since it might be difficult to find I'll help a bit: The datasheet will state that the voltages at the uC's inputs/outputs cannot exceed the voltage on the VDD pins. The reason for this is the ESD protection diodes. As soon as the voltage at AREF becomes higher than VDD + 0.5 V the AREF's ESD diode will start conducting. If you want a 5 V input range either power the uC with 5 V or use a voltage divider to lower the input voltage to the ADC.
– Bimpelrekkie
2 days ago






Indeed this information will be in the datasheet, but since it might be difficult to find I'll help a bit: The datasheet will state that the voltages at the uC's inputs/outputs cannot exceed the voltage on the VDD pins. The reason for this is the ESD protection diodes. As soon as the voltage at AREF becomes higher than VDD + 0.5 V the AREF's ESD diode will start conducting. If you want a 5 V input range either power the uC with 5 V or use a voltage divider to lower the input voltage to the ADC.
– Bimpelrekkie
2 days ago














Thank you! I’ll use a voltage divider as it’s the best solution in my case.
– Petru-Sebastian Toader
2 days ago




Thank you! I’ll use a voltage divider as it’s the best solution in my case.
– Petru-Sebastian Toader
2 days ago




2




2




To learn more about what issues the ESD diodes can cause, watch this EEVBlog video: youtube.com/watch?v=2yFh7Vv0Paw Making this and comment above an answer because, well it is.
– Bimpelrekkie
2 days ago






To learn more about what issues the ESD diodes can cause, watch this EEVBlog video: youtube.com/watch?v=2yFh7Vv0Paw Making this and comment above an answer because, well it is.
– Bimpelrekkie
2 days ago












1 Answer
1






active

oldest

votes


















6














Indeed this information will be in the datasheet, but since it might be difficult to find I'll help a bit:



The datasheet will state that the voltages at the uC's inputs/outputs cannot exceed the voltage on the VDD pins.



The reason for this is the ESD protection diodes. As soon as the voltage at AREF becomes higher than VDD + 0.5 V the AREF's ESD diode will start conducting.



So if you connect 5 V to AREF, the VDD supply of the uC will be pulled up to about 4.4 V ! But you supplied 3.3 V via an LDO. Yes, then the LDO will do nothing.



If you want a 5 V input range either power the uC with 5 V



or



use a voltage divider to lower the input voltage to the ADC.



To learn more about what issues the ESD diodes can cause, watch this EEVBlog video






share|improve this answer





















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    1 Answer
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    1 Answer
    1






    active

    oldest

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    active

    oldest

    votes






    active

    oldest

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    6














    Indeed this information will be in the datasheet, but since it might be difficult to find I'll help a bit:



    The datasheet will state that the voltages at the uC's inputs/outputs cannot exceed the voltage on the VDD pins.



    The reason for this is the ESD protection diodes. As soon as the voltage at AREF becomes higher than VDD + 0.5 V the AREF's ESD diode will start conducting.



    So if you connect 5 V to AREF, the VDD supply of the uC will be pulled up to about 4.4 V ! But you supplied 3.3 V via an LDO. Yes, then the LDO will do nothing.



    If you want a 5 V input range either power the uC with 5 V



    or



    use a voltage divider to lower the input voltage to the ADC.



    To learn more about what issues the ESD diodes can cause, watch this EEVBlog video






    share|improve this answer


























      6














      Indeed this information will be in the datasheet, but since it might be difficult to find I'll help a bit:



      The datasheet will state that the voltages at the uC's inputs/outputs cannot exceed the voltage on the VDD pins.



      The reason for this is the ESD protection diodes. As soon as the voltage at AREF becomes higher than VDD + 0.5 V the AREF's ESD diode will start conducting.



      So if you connect 5 V to AREF, the VDD supply of the uC will be pulled up to about 4.4 V ! But you supplied 3.3 V via an LDO. Yes, then the LDO will do nothing.



      If you want a 5 V input range either power the uC with 5 V



      or



      use a voltage divider to lower the input voltage to the ADC.



      To learn more about what issues the ESD diodes can cause, watch this EEVBlog video






      share|improve this answer
























        6












        6








        6






        Indeed this information will be in the datasheet, but since it might be difficult to find I'll help a bit:



        The datasheet will state that the voltages at the uC's inputs/outputs cannot exceed the voltage on the VDD pins.



        The reason for this is the ESD protection diodes. As soon as the voltage at AREF becomes higher than VDD + 0.5 V the AREF's ESD diode will start conducting.



        So if you connect 5 V to AREF, the VDD supply of the uC will be pulled up to about 4.4 V ! But you supplied 3.3 V via an LDO. Yes, then the LDO will do nothing.



        If you want a 5 V input range either power the uC with 5 V



        or



        use a voltage divider to lower the input voltage to the ADC.



        To learn more about what issues the ESD diodes can cause, watch this EEVBlog video






        share|improve this answer












        Indeed this information will be in the datasheet, but since it might be difficult to find I'll help a bit:



        The datasheet will state that the voltages at the uC's inputs/outputs cannot exceed the voltage on the VDD pins.



        The reason for this is the ESD protection diodes. As soon as the voltage at AREF becomes higher than VDD + 0.5 V the AREF's ESD diode will start conducting.



        So if you connect 5 V to AREF, the VDD supply of the uC will be pulled up to about 4.4 V ! But you supplied 3.3 V via an LDO. Yes, then the LDO will do nothing.



        If you want a 5 V input range either power the uC with 5 V



        or



        use a voltage divider to lower the input voltage to the ADC.



        To learn more about what issues the ESD diodes can cause, watch this EEVBlog video







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered 2 days ago









        BimpelrekkieBimpelrekkie

        47.3k240104




        47.3k240104






























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