mc145170-2 Freescale Semiconductor, Inc, mc145170-2 Datasheet - Page 20

• Manufacturer Part Number: mc145170-2
• Description: Pll Frequency Synthesizer With Serial Interface
• Manufacturer: Freescale Semiconductor, Inc

Design Considerations
20
NOTES:
Denifitions:
N = Total Division Ratio in Feedback Loop
K
K
For a nominal design starting point, the user might consider a damping factor ζ = 0.7 and a natural loop
frequency ω
in faster loop lock times and, for similar sideband filtering, higher f
K VCO VCO Gain
φ
φ
(Phase Detector Gain) = VDD/4p volts per radian for PDout
(Phase Detector Gain) - VDD/2p volts per radian for fV and fR
1.
2.
(
For (C), R
then placed from the midpoint to ground to further filter the error pulses. The value of C
corner frequency of this network does not significantly affect ω
The φ
mode input range of the op amp.
(A)
(B)
(C)
R
n
and φ
= (2πf
PD
φ
φ
)
1
PD
R
V
out
=
is frequently split into two series resistors; each resistor is equal to R
out
V
2π∆f VCO
--------------------------
∆V VCO
outputs swing rail-to-rail. Therefore, the user should be careful not to exceed the common
R
R
/50) where f
1
R
1
C
Figure 23. Phase-Locked Loop - Low Pass Filter Design
C
R
R
1
1
R
C
2
VCO
VCO
R
2
R
+
-
is the frequency at the phase detector input. Larger ω
MC145170-2 Technical Data, Rev. 5
R
A
2
MC33077 or
equivalent
(Note 3)
C
VCO
n
ω n
ζ
F s ( )
ω n
ζ
F s ( )
ω n
ζ
F s ( )
.
=
=
=
=
=
=
---------------------------- -
2K
0.5ω n R 2 C
ω n R 2 C
--------------------
=
=
=
φ
Nω n
K φ K VCO
-------------------------
------------------------- -
R 1 sC
----------------------------------- -
NC R 1
-------------------------------------------- -
(
K φ K VCO
-------------------------
2
R 2 sC
------------------------- -
K VCO
R 1
NR 1 C
NCR 1
K φ K VCO
R 1 sC
⎛
⎝
R
(
R 2 sC
1
+
-related VCO standards.
R 2
+
+
+
1
1
+
)sC
R 2
+
-------------------------
K φ K VCO
1
1
)
divided by 2. A capacitor C
+
N
1
C
⎞
⎠
should be such that the
Freescale Semiconductor
n
values result
C
is