TRK-USB-MPC5643L Freescale Semiconductor, TRK-USB-MPC5643L Datasheet - Page 94

• Manufacturer Part Number: TRK-USB-MPC5643L
• Description: Development Boards & Kits - Other Processors StarTrakMiniUSG MPC5643L
• Manufacturer: Freescale Semiconductor

Specifications of TRK-USB-MPC5643L

• Rohs: yes
• Product: Starter Kits
• Tool Is For Evaluation Of: MPC5643L
• Core: Five Stage Pipeline
• Interface Type: LIN, DSPI
• Operating Supply Voltage: 3 V to 3.6 V
• Data Bus Width: 32 bit, 64 bit
• Description/function: Starter Kit for MPC5643L
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 40 C
• For Use With: MPC5643L

Electrical characteristics
3.15.1
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
be measured. The filter at the input pins must be designed taking into account the dynamic characteristics of the input signal
(bandwidth) and the equivalent input impedance of the ADC itself.
In fact a current sink contributor is represented by the charge sharing effects with the sampling capacitance: C
substantially a switched capacitance, with a frequency equal to the conversion rate of the ADC, it can be seen as a resistive path
to ground. For instance, assuming a conversion rate of 1 MHz, with C
(R
voltage partitioning between this resistance (sampled voltage on C
designed to respect the
94
EQ
= 1 / (f
C
Input Impedance and ADC Accuracy
 C
S
), where fc represents the conversion rate at the considered channel). To minimize the error induced by the
code out
Equation
4095
4094
4093
4092
4091
4090
Offset Error OSE
7
6
5
4
3
2
1
0
Figure 7. ADC characteristics and error definitions
4:
1
2
MPC5643L Microcontroller Data Sheet, Rev. 8.1
3
4
1 LSB (ideal)
5
V A
6

7
(3)
R S
-------------------- -
(5)
R EQ
( 2)
+
(4)
R F
V
4089 4090 4091 4092 4093 4094 4095
in(A)

(LSB
1
-- - LSB
2
( 1)
(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
S
) and the sum of R
ideal
S
1 LSB ideal =(VrefH-VrefL)/ 4096 =
3.3V/ 4096 = 0.806 mV
Total Unadjusted Error
TUE = +/- 6 LSB = +/- 4.84mV
equal to 7.5 pF, a resistance of 133 k is obtained
)
Offset Error OSE
S
Gain Error GE
+ R
F
, the external circuit must be
Freescale Semiconductor
S
being
Eqn. 4