mpc5604p Freescale Semiconductor, Inc, mpc5604p Datasheet - Page 42

• Manufacturer Part Number: mpc5604p
• Description: Mpc5604p Microcontroller Data Sheet
• Manufacturer: Freescale Semiconductor, Inc

In particular two different transient periods can be distinguished:
42
•
•
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
7:
1
Figure 7. Transient Behavior during Sampling Phase
P2
is redistributed also on C
Voltage Transient on C
V A1
Preliminary—Subject to Change Without Notice
MPC5604P Microcontroller Data Sheet, Rev. 3
•
2
(
C S
τ 1
τ 1
τ 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
ΔV < 0.5 LSB
t
= C
)
)
were in parallel to C
V A
•
•
C S T S
+
P1
-------------------- -
C P
C P C S
τ
C P2
P1
1
•
+ C
«
τ
+
•
< (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
Freescale Semiconductor
P
A1
and C
on the capacitance
S
are in series,
S
occurs (C
Eqn. 5
Eqn. 6
Eqn. 7
Eqn. 8
S
S