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TM4C internal LDO output calibration

Victor Zheng
Intellectual 1550 points


All

Do we have any method to calibrate the output of LDO integrated in TM4C. I want to use it as the reference of ADC. Thank you.

Victor

  • 0
    Guru 10570 points
    Can that LDO even supply the current necessary for the reference?

    I also would not necessarily expect it to be sufficiently stable to act as a reference.

    Robert
  • 0
    TI__Guru**** 244440 points
    Hello Victor

    The internal LDO is pre-calibrated and cannot be re-calibrated. Also you cannot use the internal LDO as the reference for ADC since (1) Using it as a reference may cause excessive current sink during high speed operation of the device and ADC conversion causing voltage drops making it unsuitable for ADC reference and (2) the voltage is outside the reference voltage range for ADC.
  • 0 in reply to Amit Ashara
    TI__Intellectual 1550 points
    Thank you Amit
    Victor
  • 0 in reply to Victor Zheng
    Guru 13040 points
    Gents,

    Just as a further consideration, this is generally how we've been dealing with voltage references:

    - On chips that have a separate VREF input and the analog signals can be chopped to a max of 3.0V, we use a 3.0V REF LDO chip powered from the main 3V3 power bus.
    - On chips without a separate VREF (smaller TM4C123x), we have two power supplies on the board: one is a more stable reference that is used for VDDA at 3.3V, and the other is the general 3.3V power supply for VDDC (which is enabled only AFTER VDDA crosses 3.1V).
    - On projects that demand more precise ADC, there are usually external dedicated ADC and references, and still we'd use one of the external references into the VREF input, so that system conditions can be monitored.

    Of course, if the precision level ain't too strict (simply monitor the battery level to indicate low bat, for example), the main 3V3 circuit is probably good enough and can be assumed 3V3.

    Anyway, this might not add much, but I just wanted to leave the notes here and open for suggestions/discussions if anyone feels like.
    Bruno