LMX2485 National Semiconductor Corporation, LMX2485 Datasheet - Page 34

• 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

www.national.com
REGISTER
Programming Description
2.7 R6 REGISTER
2.7.1 RF_TOC -- RF Time Out Counter and Control for FLoutRF Pin
The RF_TOC[13:0] word controls the operation of the RF Fastlock circuitry as well as the function of the FLoutRF output pin.
When this word is set to a value between 0 and 3, the RF Fastlock circuitry is disabled and the FLoutRF pin operates as a general
purpose CMOS TRI-STATE I/O. When RF_TOC is set to a value between 4 and 16383, the RF Fastlock mode is enabled and
the FLoutRF pin is utilized as the RF Fastlock output pin. The value programmed into the RF_TOC[13:0] word represents two
times the number of phase detector comparison cycles the RF synthesizer will spend in the Fastlock state.
2.7.2 RF_CPF -- RF PLL Fastlock Charge Pump Current
Specify the charge pump current for the Fastlock operation mode for the RF PLL. Note that the Fastlock charge pump current,
steady state current, and CSR control are all interrelated.
R6
RF_TOC
16383
RF_CPF
…
0
1
2
3
4
5
10
11
12
13
14
15
0
1
2
3
4
5
6
7
8
9
23
CSR[1:0]
22
Fastlock Mode
21
RF_CPF[3:0]
Disabled
Disabled
Disabled
Enabled
Enabled
Enabled
Enabled
Manual
RF Charge Pump State
20
19
10X
11X
12X
13X
14X
15X
16X
1X
2X
3X
4X
5X
6X
7X
8X
9X
18
17
(Continued)
16
Fastlock Period [CP events]
DATA[19:0]
15
16383X2 = 32766
14
5X2 = 10
4X2 = 8
34
N/A
N/A
N/A
N/A
…
13
Typical RF Charge Pump Current at 3 Volts (µA)
RF_TOC[13:0]
12
11
10
9
8
1045
1235
1330
1425
1520
Forces all Fastlock conditions
1140
190
285
380
475
570
665
760
855
950
FLoutRF Pin Functionality
95
7
6
High Impedance
Logic “0” State.
Logic “0” State
Logic “1” State
5
Fastlock
Fastlock
Fastlock
Fastlock
4
C3
3
1
C2
2
1
C1
1
0
C0
0
1