XC68HC08KH12 Motorola, XC68HC08KH12 Datasheet - Page 111

• Manufacturer Part Number: XC68HC08KH12
• Description: MICROCONTROLLER
• Manufacturer: Motorola

8.9.3 Choosing a Filter Capacitor
8.9.4 Reaction Time Calculation
MC68HC(7)08KH12
MOTOROLA
—
Rev. 1.0
As described in
external filter capacitor, C
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 the value of V
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 percent 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:
The K factor in the equations is derived from internal PLL parameters.
K
K
8.4.4 Acquisition and Tracking
ACQ
TRK
•
•
•
•
is the K factor when the PLL is configured in tracking mode. (See
is the K factor when the PLL is configured in acquisition mode, and
Correct selection of filter capacitor, C
Filter
Room temperature operation
Negligible external leakage on CGMXFC
Negligible noise
Clock Generator Module (CGM)
Capacitor.)
8.9.2 Parametric Influences on Reaction
DDA
, choose the voltage potential at which the MCU is
F
, is critical to the stability and reaction time of
C
F
=
C
FACT
Modes.) Reaction time is based on
V
------------ -
f
RDV
DDA
Acquisition/Lock Time Specifications
F
(See
Clock Generator Module (CGM)
8.9.3 Choosing a
Advance Information
Time, the
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