mc68hc08az60 Freescale Semiconductor, Inc, mc68hc08az60 Datasheet - Page 129

• Manufacturer Part Number: mc68hc08az60
• Description: M68hc08 Family Of 8-bit Microcontroller Units Mcus
• Manufacturer: Freescale Semiconductor, Inc

Choosing a Filter
Capacitor
Reaction Time
Calculation
25-cgm
MOTOROLA
filter capacitor, filter capacitor leakage, stray impedances on the circuit
board, and even humidity or circuit board contamination.
As described in
128, the external filter capacitor, C
time of the PLL. The PLL is also dependent on reference frequency and
supply voltage. The value of the capacitor must, therefore, be chosen
with supply potential and reference frequency in mind. For proper
operation, the external filter capacitor must be chosen according to this
equation:
For acceptable values of C
408). For the value of V
MCU is operating. If the power supply is variable, choose a value near
the middle of the range of possible supply values.
This equation does not always yield a commonly available capacitor
size, so round to the nearest available size. If the value is between two
different sizes, choose the higher value for better stability. Choosing the
lower size may seem attractive for acquisition time improvement, but the
PLL may become unstable. Also, always choose a capacitor with a tight
tolerance ( 20% or better) and low dissipation.
The actual acquisition and lock times can be calculated using the
equations below. These equations yield nominal values under the
following conditions:
Freescale Semiconductor, Inc.
•
•
•
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For More Information On This Product,
Correct selection of filter capacitor, C
Capacitor
Room temperature operation
Negligible external leakage on CGMXFC
Negligible noise
Clock Generator Module (CGM)
Go to: www.freescale.com
Parametric Influences on Reaction Time
on page 129).
DDA
C
fact
, choose the voltage potential at which the
F
, (see
=
C
F
fact
, is critical to the stability and reaction
Electrical Specifications
V
------------ -
f
DDA
rdv
Acquisition/Lock Time Specifications
F
Clock Generator Module (CGM)
(see
MC68HC08AZ60 — Rev 1.0
Choosing a Filter
on page
on page
129