LMX2487E National Semiconductor Corporation, LMX2487E Datasheet - Page 29

• Manufacturer Part Number: LMX2487E
• Description: 7.5 Ghz High Performance Delta-sigma Low Power Dual Pllatinum? Frequency Synthesizers With 3.0 Ghz Integer Pll
• Manufacturer: National Semiconductor Corporation

2.4 R3 REGISTER
REGISTER
2.4.1 IF_R[11:0] -- IF R Divider Value
For the IF R divider, the R value is determined by the IF_R[11:0] bits in the R3 register. The minimum value for IF_R is 3.
2.4.2 RF_CPG -- RF PLL Charge Pump Gain
This is used to control the magnitude of the RF PLL charge pump in steady state operation.
2.4.3 ACCESS -- Register Access word
It is mandatory that the first 5 registers R0-R4 be programmed. The programming of registers R5-R7 is optional. The ACCESS
[3:0] bits determine which additional registers need to be programmed. Any one of these registers can be individually programmed.
According to the table below, when the state of a register is in default mode, all the bits in that register are forced to a default state
and it is not necessary to program this register. When the register is programmable, it needs to be programmed through the
MICROWIRE. Using this register access technique, the programming required is reduced up to 37%.
The default conditions the registers is shown below:
R Value
4095
...
3
R3
0
1
.
ACCESS Bit
ACCESS[0]
ACCESS[1]
ACCESS[2]
ACCESS[3]
23
RF_CPG
ACCESS[3:0]
10
11
12
13
14
15
0
1
2
3
4
5
6
7
8
9
22
0
1
.
21
20
0
1
.
19
RF_CPG[3:0]
18
0
1
.
17
16
0
1
Charge Pump State
.
Register Location
DATA[19:0]
15
R3[20]
R3[21]
R3[22]
R3[23]
10X
11X
12X
13X
14X
15X
16X
14
1X
2X
3X
4X
5X
6X
7X
8X
9X
29
IF_R[11:0]
0
1
.
13
12
0
1
.
IF_R[11:0]
11
0
1
.
10
Typical RF Charge Pump Current at 3
9 8 7 6 5 4
0
1
.
Register Controlled
Must be set to 1
Volts (µA)
0
1
.
1045
1140
1235
1330
1425
1520
190
285
380
475
570
665
760
855
950
R5
R6
R7
95
C3
3
0
1
1
.
C2
2
1
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C1
1
1
1
1
.
C0
0
1