Motorola MPC533 Reference Manual page 1088

Crystal Oscillator External Components
C is load capacitance
L
C is pad capacitance
PAD
• XTAL pad capacitance is C
• EXTAL pad capacitance is C
C is socket and board trace capacitance
SOCKET
• Socket capacitance C <=1pF
• Board trace capacitance C <=1pF. This should be low since the crystal must be
located very close to the chip.
I.3.1 KAPWR Filtering
The KAPWR signal is the MPC533 keep-alive power. KAPWR is used for the crystal
oscillator circuit, and should be isolated from the noisy supplies. It is recommended that an
RC filter be used on KAPWR, or bypass capacitors that are located as close as possible to
the part.
KAP 2.6 V
Note: A filter cut off frequency of 500Hz is recommended, however this will result in a
capacitor size of 33uF using a 10 Ohm resistor. This may be too expensive or large
for the system. In this case the filter shown with cut- off frequency of 160kHz will suffice.
KAP 2.6 V
Figure I-4. Bypass Capacitors Example (Alternative)
I-4
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
= ~7 pF
PAD
= ~7 pF
PAD
Board
<40 Ω
100 nF
VSSSYN
Figure I-3. RC Filter Example
Board
100 nF
1 µF
VSSSYN
MPC533 Reference Manual
MPC53x Device
KAPWR
MPC53x Device
KAPWR
MOTOROLA