mpc5602d Freescale Semiconductor, Inc, mpc5602d Datasheet - Page 53

• Manufacturer Part Number: mpc5602d
• Description: Mpc5602d Microcontroller Data Sheet
• Manufacturer: Freescale Semiconductor, Inc

possible, ideally infinite. This capacitor contributes to attenuating the noise present on the input pin; furthermore, 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
= 1 / (f
partitioning between this resistance (sampled voltage on C
must be designed to respect the
Freescale Semiconductor
c
*C
S
), where f
c
represents the conversion rate at the considered channel). To minimize the error induced by the voltage
Equation
Preliminary—Subject to Change Without Notice
MPC5602D Microcontroller Data Sheet, Rev. 3.1
V A
4:

R S
-------------------------------------------------------------------------- -
+
R F
+
R L
R EQ
S
) and the sum of R
+
R SW
+
S
R AD
equal to 3 pF, a resistance of 330 k is obtained (R

S
1
-- - LSB
2
+ R
F
+ R
L
+ R
SW
+ R
Electrical characteristics
AD
, the external circuit
S
being
Eqn. 4
EQ
53