LMX1501 National Semiconductor, LMX1501 Datasheet - Page 17

• Manufacturer Part Number: LMX1501
• Description: PLLatinumTM 1.1 GHz Frequency Synthesizer for RF Personal Communications
• Manufacturer: National Semiconductor

Application Information
Example
K
K
RF
F
N
ATTEN
if we choose R3
Converting to standard component values gives the follow-
ing filter values which are shown in Figure 4
Note 1 See related equation for K in Charge Pump Current Specification
VCO
ref
p
p
C1
R2
C2
R3
C3
e
opt
e
e
e
e
RF
e
e
e
e
e
43
e
5 mA (Note 1)
2
e
Definitions For this example V
be approximated using the curves in the Typical Performance Char-
acteristics for Charge Pump Current vs D
are in mA You may also use K
you must convert K
25 kHz
T1
T3
T2
C1
C2
R2
opt
e
2200 pF
8 2 k
0 018 F
120 k
78 pF
19 3 MHz V
886 MHz
c
10 dB
e
e
e
e
e
e
e
e
e
5 kHz
1
f
ref
sec
(1 8101e4)
1 8101e4
1 318e
2 153 nF
2 153 nF
1 318e
18 35e
(1 38e
1 38e
e
10
(2
e
e
35440
(10 20)
p
1
b
120k then C3
3 1415e4
b
b
b
b
b
a
p
VCO
25e3)
5
(tan 43 ) (1 38e
4
5
4
9
tan
(1 38e
2
(1 8101e4)
1 318e
1 384e
e
a
b
to (rad V) multiplying by 2
(5e
9 361e
(1 38e
7 18 k
p
2
1
e
b
P
b
e
(tan 43 ) (1 38e
b
b
e
1
1 38e
5
e
3) 19 3e6
9 361e
4
5
b
5 0V The value for K can then
a
b
(5 mA 2
e
2
b
5
6)
9 361e
9 361e
b
a
o
1
b
2
(35440)
120e3
Voltage The units for K
5
(Continued)
b
a
5
9 361e
e
6
a
1 38e
rad) but in this case
b
b
18 35 nF
9 361e
6)
6
b
b
2
e
b
5
a
6)
1
5 9 361e
a
78 pF
b
1 38e
e
a
9 361e
6)
1 318e
(1 8101e4)
b
5 9 361e
b
b
17
b
6)
6
4
2
2
1
a
(1 38e
b
(1 8101e4)
6
b
b
1
5)
2
FIGURE 4 E 5 kHz Loop Filter
2
1
a
(1 318e
(1 8101e4)
b
4)
2
2
(9 361e
b
6)
2
TL W 12340– 41