The total calibration conversion time is: 12 × ( # of AVERAGE × [Sample time(sample + 1) + 1 cycle for hold + 34 cycles for compare phase]) + 1st conversionsynchronization (~5 ADC cycles + 5 module clocks).For high accuracy of the ADC (as specified in data sheet) on your application board(PCB), the following requirements should be met:• Bypass caps between VREFH and VREFL. Suggested cap sizes: 1 nF, 100 nF,10 μF.• Place caps on PCB as close as possible to the device pins VREFH and VREFL.• Bypass caps between VDDA and VSSA. Suggested cap sizes: 1 nF, 100 nF, 10 μF.• Place caps on PCB as close as possible to the device pins VDDA and VSSA.• Routing of VDDA, VSSA, VREFH, and VREFL on PCB:• Low impedance between the bypass caps and the MCU pins.• Keep routing distant from noisy signal routes like switching I/Os.38.5.7 User-defined offset functionOFS is a two's-complement, left-justified register that contains the calibration-generatedoffset error correction value.The value in OFS is subtracted from the conversion and the result is transferred into theresult registers, Rn. If the result is greater than the maximum or less than the minimumresult value, it is forced to the appropriate limit for the current mode of operation.The formatting of OFS is different from the data result register, Rn, to preserve theresolution of the calibration value regardless of the conversion mode selected. Lowerorder bits are ignored in lower resolution modes. For example, in 8-bit single-endedmode, OFS[14:7] are subtracted from D[7:0]; OFS[15] indicates the sign (negativenumbers are effectively added to the result) and OFS[6:0] are ignored.OFS is automatically set according to calibration requirements after the self-calibrationsequence is done, that is, SC3[CAL] is cleared. You can write to OFS to override thecalibration result if desired. If you write an OFS value that is different from thecalibration value, the ADC error specifications may not be met. You should store thevalue generated by the calibration function in memory before overwriting with a user-specified value.NoteThere is an effective limit to the values of offset that you canset. If the magnitude of the offset is too high, the results of theconversions will cap off at the limits.Chapter 38 Analog-to-Digital Converter (ADC)MWCT101xS Series Reference Manual, Rev. 3, 07/2019NXP Semiconductors 1045
