MPC5643L_11 datasheet(87/124 Pages) FREESCALE

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Electrical characteristics

MPC5643L Microcontroller Data Sheet, Rev. 6

Preliminary—Subject to Change Without Notice

Freescale Semiconductor

3.14

16 MHz RC oscillator electrical characteristics

3.15

ADC electrical characteristics

The device provides a 12-bit Successive Approximation Register (SAR) Analog-to-Digital Converter.

Figure 7. ADC characteristics and error definitions

3.15.1

Input Impedance and ADC Accuracy

To preserve the accuracy of the A/D converter, it is necessary that analog input pins have low AC impedance. Placing a capacitor

with good high frequency characteristics at the input pin of the device can be effective: the capacitor should be as large as

possible, ideally infinite. This capacitor contributes to attenuating the noise present on the input pin; further, it sources charge

during the sampling phase, when the analog signal source is a high-impedance source.

A real filter can typically be obtained by using a series resistance with a capacitor on the input pin (simple RC filter). The RC

filtering may be limited according to the value of source impedance of the transducer or circuit supplying the analog signal to

Table 22. RC oscillator electrical characteristics

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

fRC

RC oscillator frequency

TJ =25°C

—

MHz



RCMVAR

Fast internal RC oscillator variation with

respect to fRC.

——

—

±5

(2)

(1)

(3)

(4)

(5)

Offset Error OSE

Gain Error GE

1 LSB (ideal)

Vin(A) (LSBideal)

(1) Example of an actual transfer curve

(2) The ideal transfer curve

(3) Differential non-linearity error (DNL)

(4) Integral non-linearity error (INL)

(5) Center of a step of the actual transfer

curve

code out

4095

4094

4093

4092

4091

4090

4089 4090 4091 4092 4093 4094 4095

1 LSB ideal =(VrefH-VrefL)/ 4096 =

3.3V/ 4096 = 0.806 mV

Total Unadjusted Error

TUE = +/- 6 LSB = +/- 4.84mV

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