Sources Of Error - NXP Semiconductors MKL27Z128VFM4 Reference Manual

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high-frequency characteristics. This capacitor is connected between V

and must be placed as near as possible to the package pins. Resistance in the path is not

recommended because the current causes a voltage drop that could result in conversion

errors. Inductance in this path must be minimum, that is, parasitic only.

23.7.1.3 Analog input pins

The external analog inputs are typically shared with digital I/O pins on MCU devices.

Empirical data shows that capacitors on the analog inputs improve performance in the

presence of noise or when the source impedance is high. Use of 0.01 μF capacitors with

good high-frequency characteristics is sufficient. These capacitors are not necessary in all

cases, but when used, they must be placed as near as possible to the package pins and be

referenced to V

For proper conversion, the input voltage must fall between V

is equal to or exceeds V

full scale 12-bit representation, 0x3FF, which is full scale 10-bit representation, or 0xFF,

which is full scale 8-bit representation. If the input is equal to or less than V

converter circuit converts it to 0x000. Input voltages between V

straight-line linear conversions. There is a brief current associated with V

sampling capacitor is charging.

For minimal loss of accuracy due to current injection, pins adjacent to the analog input

pins must not be transitioning during conversions.

23.7.2 Sources of error

23.7.2.1 Sampling error

For proper conversions, the input must be sampled long enough to achieve the proper

RAS + RADIN =SC / (FMAX * NUMTAU * CADIN)

RAS = External analog source resistance

SC = Number of ADCK cycles used during sample window

Freescale Semiconductor, Inc.

, the converter circuit converts the signal to 0xFFF, which is

Figure 23-3. Sampling equation

KL27 Sub-Family Reference Manual , Rev. 5, 01/2016

Chapter 23 Analog-to-Digital Converter (ADC)

. If the input