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  • Case ID: 278411
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nRF5340 ADC reference and gain questions

user95520

In the nRF5340 product specification version 1.2, I see an internal bandgap reference error range of -1.8/+0.5%.

  • In the nRF5340 product specification version 1.2, I see an internal bandgap reference error range of -1.8/+0.5%.
    • Is this the same internal reference used by the ADC?
    • Is this the reference error over the recommended operating temperature range of the nRF5340?
    • I see in older RF development zone cases, such as case ID: 268846, that the room temperature reference error is +-0.2%.  Is this error still applicable to the nRF5340
    • How stable is the reference error over time?

  • The nRF5340 product specification also lists gain errors from -3% to +3% (+4% for G=0.5, G=1)
    • Is this the gain error over the recommended operating temperature range of the nRF5340?
    • How stable is the gain error over time?
    • Are gain values < 1 realized by tap points on the resistor ladder?
    • If we use a gain value < 1, is there an additional series source resistance that we have to account for when calculating minimum ADC acquisition time?
  • 0

    Hi 

    I have forwarded your questions to the hardware team, and I will let you know when I hear back from them. 

    Best regards
    Torbjørn

  • 0 in reply to user2116

    Hi Torbjorn,

    Have you received a response from the hardware team?

    Sincerely,

    Doug Young

  • 0 in reply to user95520

    Hi Doug

    I haven't gotten a response yet unfortunately. I have asked the team if they can provide a schedule for when this work can be done. 

    Best regards
    Torbjørn

  • 0

    Hi Torbjorn,

    Do you have any updates or a schedule from the team as to when this will be addressed?

    Sincerely,

    Doug Young

  • 0

    Hi Doug

    I am very sorry for the slow response. You will find a response to your questions below:

    In the nRF5340 product specification version 1.2, I see an internal bandgap reference error range of -1.8/+0.5%.
    • Is this the same internal reference used by the ADC?

    No, the referred reference is used for the COMP peripheral, not the ADC. 

    Is this the reference error over the recommended operating temperature range of the nRF5340?

    Reference error is accounted in Gain error parameters in the product specification (SAADC Electrical specification chapter), and the gain error temperature coefficient is given by the C_EG parameter. 

    I see in older RF development zone cases, such as case ID: 268846, that the room temperature reference error is +-0.2%.  Is this error still applicable to the nRF5340

    Yes, the case you refer to is for the nRF5340. 

    How stable is the reference error over time?

    If the temperature and voltage is stable the reference should have negligible variation. 

    The nRF5340 product specification also lists gain errors from -3% to +3% (+4% for G=0.5, G=1)
    • Is this the gain error over the recommended operating temperature range of the nRF5340?

    No. As stated in the footnote in the product specification, temperature is not included. You have a dedicated parameter for the gain error temperature coefficient. 

    How stable is the gain error over time?

    Gain error is stable as long as voltage and temperature stay unchanged. 

    Are gain values < 1 realized by tap points on the resistor ladder?

    No

    If we use a gain value < 1, is there an additional series source resistance that we have to account for when calculating minimum ADC acquisition time?

    No. Section 7.29.9 in the product specification applies independently of gain setting. 

    Best regards
    Torbjørn

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