LMX2346 National Semiconductor Corporation, LMX2346 Datasheet - Page 23

• Manufacturer Part Number: LMX2346
• Description: Pllatinum? Frequency Synthesizer For Rf Personal Communications
• Manufacturer: National Semiconductor Corporation

2.0 Programming Description
2.2.1 R_CTR[9:0]
The reference divider can be programmed to support divide ratios from 2 to 1023. Divide ratios of less than 2 are prohibited.
2.2.2 CP_TRI
The CP_TRI control bit allows the charge pump to be switched between a normal operating mode and a high impedance output
state. This happens asynchronously or immediately with the change in CP_TRI bit.
2.2.3 PD_POL
The PD_POL control bit is used to set the polarity of the phase detector based on the VCO tuning characteristic.
2.2.4 LD_OUT[1:0]
The LD_Out control word is used to select which signal is routed the the LD pin.
Reference Divider Ratio
Control Bit
CP_TRI
Control Bit
PD_POL
1,023
2
3
•
Charge Pump TRI-STATE
Phase Detector Polarity
Reference Divider (R COUNTER)
LD Output Select
LD_OUT[1:0]
Register Location
0
1
2
3
Register Location
R[11]
9
0
0
1
R[12]
•
R[14:13]
8
0
0
1
•
R[12]
R[11]
(Continued)
VCO Characteristics
LD Pin Output Mode
Analog Lock Detect
Digital Lock Detect
R divider output
N divider output
Phase Detector
7
0
0
1
•
Charge Pump
Description
Description
TRI-STATE
Polarity
R[10:1]
23
6
0
0
1
•
R_CNTR [9:0]
5
0
0
1
•
Negative VCO Tuning
Charge Pump Operates
20038409
Characteristic
4
0
0
1
•
Normal
0
Output Circuit
Configuration
0
Open-Drain
Push-Pull
Push-Pull
Push-Pull
3
0
0
1
Function
•
Function
Positive VCO Tuning
2
0
0
1
•
Characteristic
Charge Pump Output
in High Impedance
1
1
1
1
1
•
State
1
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0
0
1
1
•