LMX2485 National Semiconductor Corporation, LMX2485 Datasheet - Page 33

• Manufacturer Part Number: LMX2485
• Description: 50 Mhz - 3.0 Ghz High Performance Delta-sigma Low Power Dual Pllatinum 50 Mhz - 3.0 Ghz High Performance Delta-sigma Low Power Dual Pllatinum? Frequency Synthesizers With 800 Mhz Integer Pll
• Manufacturer: National Semiconductor Corporation

REGISTER
Programming Description
2.6 R5 REGISTER
2.6.1 Fractional Numerator Determination { RF_FN[21:12], RF_FN[11:0], ACCESS[1] }
In the case that the ACCESS[1] bit is 0, then the part operates in 12-bit fractional mode, and the RF_FN2[21:12] bits become do
not care bits. When the ACCESS[1] bit is set to 1, the part operates in 22-bit mode and the fractional numerator is expanded from
12 to 22-bits.
2.6.2 Fractional Denominator Determination { RF_FD[21:12], RF_FD[11:0], ACCESS[1]}
In the case that the ACCESS[1] bit is 0, then the part is operates in the 12-bit fractional mode, and the RF_FD[21:12] bits become
do not care bits. When the ACCESS[1] is set to 1, the part operates in 22-bit mode and the fractional denominator is expanded
from 12 to 22-bits.
Denominator
Numerator
Fractional
R5
4194303
Fractional
4194303
4095
4096
4095
4096
...
...
0
1
...
...
0
1
23
0
1
.
22
0
1
.
0
1
21
.
( These bits only apply in 22- bit mode)
In 12- bit mode, these are do not care.
0
1
.
( These bits only apply in 22- bit mode)
In 12- bit mode, these are do not care.
20
these bits should be all set to 0.
0
1
.
In 22- bit mode, for N
these bits should be all set to 0.
RF_FD[21:12]
0
1
In 22- bit mode, for N
.
19
0
1
.
0
1
RF_FN[21:12]
.
18
RF_FD[21:12]
0
1
.
0
1
.
17
(Continued)
0
1
.
0
1
.
16
<
0
1
.
4096,
DATA[19:0]
<
15
0
1
.
4096,
0
1
.
14
0
1
.
33
0
1
13
.
0
1
.
12
1
1
.
1
1
.
11
0
0
1
0
1
.
.
0
0
1
0
1
.
.
RF_FN[21:12]
10
0
0
1
0
1
.
.
0
0
1
0
1
.
.
0
0
1
0
1
.
.
9
0
0
1
0
1
.
.
0
0
1
0
1
8
.
.
0
0
1
0
1
.
.
7
0
0
1
0
1
.
.
RF_FN[11:0]
0
0
1
0
1
.
.
RF_FD[11:0]
6
0
0
1
0
1
.
.
0
0
1
0
1
.
.
5
0
0
1
0
1
.
.
0
0
1
0
1
.
.
4
0
0
1
0
1
.
.
0
0
1
0
1
.
.
C3
3
1
0
0
1
0
1
.
.
0
0
1
0
1
.
.
C2
0
0
1
0
1
2
0
0
0
1
0
1
.
.
www.national.com
.
.
0
0
1
0
1
0
0
1
0
1
.
.
C1
.
.
1
1
0
1
1
0
1
0
1
1
0
1
.
.
.
.
C0
0
1