XC908AS60ACFU Motorola Semiconductor Products, XC908AS60ACFU Datasheet - Page 193

• Manufacturer Part Number: XC908AS60ACFU
• Description: MC68HC908AZ60A, MC68HC908AS60A Hcmos Microcontroller Unit Technical Data
• Manufacturer: Motorola Semiconductor Products

10.10.3 Choosing a Filter Capacitor
10.10.4 Reaction Time Calculation
MC68HC908AZ60A — Rev 2.0
MOTOROLA
Temperature and processing also can affect acquisition time because
the electrical characteristics of the PLL change. The part operates as
specified as long as these influences stay within the specified limits.
External factors, however, can cause drastic changes in the operation of
the PLL. These factors include noise injected into the PLL through the
filter capacitor, filter capacitor leakage, stray impedances on the circuit
board, and even humidity or circuit board contamination.
As described in
192, 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
530). 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:
Clock Generator Module (CGM)
Parametric Influences on Reaction Time
DDA
C
fact
F
, choose the voltage potential at which the
=
, (see
C
fact
F
, is critical to the stability and reaction
Electrical Specifications


------------------ -
f
C G M R D V
V
DDA
Acquisition/Lock Time Specifications
Clock Generator Module (CGM)


Technical Data
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