mpc5604e Freescale Semiconductor, Inc, mpc5604e Datasheet - Page 39

• Manufacturer Part Number: mpc5604e
• Description: Mpc5604e Microcontroller Data Sheet
• Manufacturer: Freescale Semiconductor, Inc

In particular two different transient periods can be distinguished:
Freescale Semiconductor
•
•
A first and quick charge transfer from the internal capacitance C
is supposed initially completely discharged): considering a worst case (since the time constant in reality would be
faster) in which C
and the time constant is
Equation 5
faster, but the A/D converter circuitry has been designed to be robust also in the very worst case: the sampling time T
is always much longer than the internal time constant:
The charge of C
according to
A second charge transfer involves also C
R
would be faster), the time constant is:
L
: again considering the worst case in which C
can again be simplified considering only C
Equation
P1
V
P2
V
V
V
CS
and C
A
A2
A1
is reported in parallel to C
Figure 11. Transient behavior during sampling phase
7:
1
P2
is redistributed also on C
Voltage Transient on C
V A1
Preliminary—Subject to Change Without Notice
MPC5604E Microcontroller Data Sheet, Rev. 2

2

C S
 1
 1
 2 R L
F
=
+

(that is typically bigger than the on-chip capacitance) through the resistance

C P1


R SW
R SW
P1

+
P2
(call C

C P2
C S
+
+
and C
S
S
T
R AD
R AD
S
, determining a new value of the voltage V
+
S

P
C P1
as an additional worst condition. In reality, the transient is
=
S
V <0.5 LSB
t
= C


were in parallel to C
V A


C S T S
+
P1
-------------------- -
C P
C P C S

C P2
P1
1

+ C
«

+

< (R

2
and C
C P1
= R
C S
P2

SW
), the two capacitances C
L

(C
+
P2
+ R
S
C P2
to the sampling capacitance C
+ C
AD
P1

P1
) C
+ C
(since the time constant in reality
S
P2
<< T
)
S
Electrical characteristics
P
A1
and C
on the capacitance
S
are in series,
S
occurs (C
Eqn. 5
Eqn. 6
Eqn. 7
Eqn. 8
39
S
S