NXP Semiconductors K32 L2A Series, Reference Manual, Page: 223 / 1379

For minimal loss of accuracy due to current injection, pins adjacent to the analog input
pins must not be transitioning during conversions.
11.6.2 Sources of error
11.6.2.1 Sampling error
For proper conversions, the input must be sampled long enough to achieve the proper
accuracy.
RAS + RADIN =SC / (FMAX * NUMTAU * CADIN)
Figure 11-3. Sampling equation
Where:
RAS = External analog source resistance
SC = Number of ADCK cycles used during sample window
CADIN = Internal ADC input capacitance
NUMTAU = -ln(LSBERR / 2
N
)
LSBERR = value of acceptable sampling error in LSBs
N = 8 in 8-bit mode, 10 in 10-bit mode, 12 in 12-bit mode or 16 in 16-bit mode
Higher source resistances or higher-accuracy sampling is possible by setting
CFG1[ADLSMP] and changing CFG2[ADLSTS] to increase the sample window, or
decreasing ADCK frequency to increase sample time.
11.6.2.2 Pin leakage error
Leakage on the I/O pins can cause conversion error if the external analog source
resistance, R
AS
, is high. If this error cannot be tolerated by the application, keep R
AS
lower than V
REFH
/ (4 × I
LEAK
× 2
N
) for less than 1/4 LSB leakage error, where N = 8 in
8-bit mode, 10 in 10-bit mode, 12 in 12-bit mode, or 16 in 16-bit mode.
Chapter 11 Analog-to-Digital Converter (ADC)
K32 L2A Reference Manual, Rev. 2, 01/2020
NXP Semiconductors 223