LMX2470 National Semiconductor Corporation, LMX2470 Datasheet - Page 34

• Manufacturer Part Number: LMX2470
• Description: 2.6 Ghz Delta-sigma Fractional-n Pll With 800 Mhz Integer-n Pll
• Manufacturer: National Semiconductor Corporation

www.national.com
REGISTER
Programming Description
2.8 R7 REGISTER
2.8.1 Fractional Numerator Determination { RF_FN2[9:0], RF_FN[11:0], FDM }
In the case that the FDM bit is 0, then the part operates in 12-bit fractional mode, and the RF_FN2 bits become don’t care bits.
When the FDM is set to 1, the part operates in 22-bit mode and the fractional numerator is expanded from 12 to 22-bits.
2.8.2 Fractional Denominator Determination { RF_FD2[9:0], RF_FD[11:0], FDM }
In the case that the FDM bit is 0, then the part is operates in the 12-bit fractional mode, and the RF_FD2 bits become don’t care
bits. When the FDM is set to 1, the part operates in 22-bit mode and the fractional denominator is expanded from 12 to 22-bits.
Numerator
Denominator
Fractional
R7
4194303
Fractional
4194303
4095
4096
4095
4096
...
...
0
1
...
...
0
1
23
0
1
.
22
0
1
.
21
0
1
.
( These bits only apply in 22- bit mode)
0
1
.
In 12- bit mode, these are don’t care.
( These bits only apply in 22- bit mode)
In 12- bit mode, these are don’t 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_FD2[9:0]
0
1
In 22- bit mode, for N
.
19
0
1
.
0
1
.
RF_FN2[9:0]
18
RF_FD2[9:0]
0
1
.
0
1
.
17
(Continued)
0
1
.
0
1
.
16
<
0
1
.
DATA[19:0]
4096,
<
15
0
1
.
4096,
0
1
.
14
0
1
.
34
13
0
1
.
0
1
.
12
1
1
.
1
1
.
11
0
0
1
0
1
.
.
0
0
1
0
1
.
.
RF_FN2[9:0]
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
1
.
.
0
0
1
0
1
.
.
0
0
1
0
1
0
0
1
0
1
.
.
C1
.
.
1
0
0
1
1
0
1
0
1
1
0
1
.
.
.
.
C0
0
1