MC68HC708XL36 FREESCALE [Freescale Semiconductor, Inc], MC68HC708XL36 Datasheet - Page 109

• Manufacturer Part Number: MC68HC708XL36
• Description: HCMOS Microcontroller Unit
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

Choosing a Filter
Capacitor
Reaction Time
Calculation
27-cgm1m_a
MOTOROLA
As described in
108, 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 the
following equation:
For acceptable values of C
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% 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
acq
•
•
•
•
Freescale Semiconductor, Inc.
is the K factor when the PLL is configured in acquisition mode, and
For More Information On This Product,
Correct selection of filter capacitor, C
Capacitor
Room temperature operation
Negligible external leakage on CGMXFC
Negligible noise
Go to: www.freescale.com
DDA
Parametric Influences on Reaction Time
on page 109.)
, choose the voltage potential at which the MCU is
CGM
C
fact
F
, (see
=
C
F
fact
, is critical to the stability and reaction
Specifications
V
------------ -
f
DDA
rdv
Acquisition/Lock Time Specifications
F
(See
Choosing a Filter
on page 333). For
MC68HC708XL36
on page
CGM
109