mc68hc908mr24 Freescale Semiconductor, Inc, mc68hc908mr24 Datasheet - Page 133

• Manufacturer Part Number: mc68hc908mr24
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

8.9.3 Choosing a Filter Capacitor
8.9.4 Reaction Time Calculation
MC68HC908MR24 — Rev. 4.1
Freescale Semiconductor
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 acceptable values of C
Specifications. For the value of V
which the 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 can 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 here. These equations yield nominal values under these
conditions:
The K factor in the equations is derived from internal PLL parameters.
K
ACQ
•
•
•
•
is the K factor when the PLL is configured in acquisition mode, and
Correct selection of filter capacitor, C
See
Room temperature operation
Negligible external leakage on CGMXFC
Negligible noise
Clock Generator Module (CGM)
8.9.3 Choosing a Filter
8.9.2 Parametric Influences on Reaction
C
F
=
F
, is critical to the stability and reaction time of
FACT
C
FACT
, see
DDA
Capacitor.
V
-------------- -
f
8.9 Acquisition/Lock Time
RDV
DDA
, choose the voltage potential at
F
Clock Generator Module (CGM)
Advance Information
Time, the
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