• State Resolved
  • Locked Locked
  • Replies 8 replies
  • Answers 2 answers
  • Subscribers 78 subscribers
  • Views 272 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

MSP430FR5969-SP: ADC Reference Calibration, Drift

Kevin Miller
Prodigy 30 points
Part Number: MSP430FR5969-SP

Hello,

We are working with the MSP430FR5969-SP and were having a tough time understanding the following.

  1. The datasheets and application notes explain that the ADC can be calibrated to the initial accuracy of the internal or external reference. There was also mention of the factory calibration keeping it within 0.5 LSB. The accuracy of the internal reference is shown to be 1.5%. Is the assumption that this is the initial accuracy, and that the ADC can be calibrated to that value within 0.5LSB?
  2. Is factory calibration an option? Or are all chips calibrated out the door?
  3. We were unable to find drift information. Is there accuracy, or bias drifting vs time we could reference? Is there a burn-in time to help speed up that initial drift to get it to a more stable value?

Thanks.

-Kevin

  • 0
    TI__Guru 56685 points

    (Edit: external reference)

    Hello,

    I'm not sure if you are referencing the following application note, but this should be helpful as well: Designing with MSP430FR58xx/FR59xx/68xx/69xx ADC

    1. Refer to section 4 in app note linked above. All factory calibration values are done with an external reference. Most of the ADC parameters in the datasheet are noted to be specified with an external reference. We only give ENOB values for ADC performance when utilizing internal reference.

    2. All devices leave factory with ADC calibration values stored in TLV area. See device datasheet details for exact conditions. Additional correction factors will be needed to be done by the customer for different temperatures or utilizing the internal reference. 

    3. I'm assuming you are speaking about the internal reference here. We do not have this data available. The specifications for the internal reference are over recommended ranges of supply voltage and operating temperature, unless otherwise noted. 

  • 0 in reply to Jace H
    Prodigy 30 points

    Thanks, Jace.

    1. I think I am still a bit confused. Is the internal reference accuracy 1.5% before calibration? Is it within 0.5LSB after calibration? Or is the accuracy only tied to the external reference, and that the overall accuracy of the ADC is 0.5LSB when using the external reference.

    2.3. Does this mean we would expect a maximum of 1.5% movement of the internal reference with temperature and time?

  • 0 in reply to Kevin Miller
    TI__Guru 56685 points

    Hello Kevin,

    1. this is discussed in section 4 in the app note I pointed to above. See quote:

    "The ADC has a gain factor and offset stored in TLV that is pre-programmed on the device based on measurements using an external reference at room temperature. When the calibration equations are applied, gain and offset error are improved as well as total unadjusted error. At room temperature, gain and offset error will be improved to ±0.5 LSB. Note the gain factor TLV value is measured with an external reference without internal buffer ADC12VRSEL = ADC12VRSEL_2, ADC12VRSEL_4, or ADC12VRSEL_14."

    2/3: Please see section 5.12.9 Reference in the datasheet for specifications on the internal reference. For ADC performance, you can see most of the parameters where specified with an external reference. Each table notes if external or internal reference is utilized for the given specifications. 

    For the highest performance with this ADC, it is recommended to utilize an external reference. Depending on your application's accuracy requirements, the performance of the ADC utilizing the internal reference can be utilized. 

  • 0 in reply to Jace H
    Prodigy 30 points

    Thanks, Jace.

    To confirm, if using the internal reference only, we can expect a 1.5% best case accuracy across time and temperature, correct?

  • 0 in reply to Kevin Miller
    Prodigy 30 points

    This is, of course, without calibrating with an external reference.

  • 0 in reply to Kevin Miller
    Prodigy 30 points

    Apologies for the triple response. Is there an easy way to specify performance if the internal reference is calibrated with an external (off board) reference, but using the internal reference for the ADC (with the external gone)? Would we still expect 1.5% over time/temp?

  • +1 in reply to Kevin Miller
    TI__Guru 56685 points

    Hello Kevin,

    You can calibrate the ADC offset error with external reference, but you won't be able to calibrate out the internal reference variance with external reference as it moves at a max of 1.5% over temp (See Table 5-32 in datasheet for exact figures).

    I would expect an improvement in performance if you were to calibrate across your temperature ranges of interest while utilizing the internal reference for the ADC. We do not specify this in our datasheet, thus I cannot give you a definitive answer on what accuracy you should expect while utilizing the ADC with internal reference. 

  • 0 in reply to Jace H
    Prodigy 30 points

    Thanks very much for all the help, Jace.

**Attention** This is a public forum