LMX2542LQ2121 NSC [National Semiconductor], LMX2542LQ2121 Datasheet - Page 19

• Manufacturer Part Number: LMX2542LQ2121
• Description: PLLatinum Cellular and GPS Frequency Synthesizer System with Integrated VCO
• Manufacturer: NSC [National Semiconductor]

Reg
R2
2.0 Programming Description
2.4 R2 REGISTER
The R2 register contains the IF_EN, IF_CUR, IF_FREQ, OSC_FREQ, and VCO_CUR control words. The register address bits
are R2[1:0] = 10. The detailed descriptions and programming information for each control word is discussed in the following
sections.
2.4.1 IF_EN - IF Synthesizer Enable (R2[2])
The IF_EN bit is used to switch the IF synthesizer between a powered up and powered down mode.
2.4.2 IF_CUR[1:0] - IF Synthesizer Charge Pump Current Gain (R2[4:3])
The IF_CUR control word is used to set the IF synthesizer’s charge pump current gain. Four gain levels are available.
2.4.3 IF_FREQ[1:0] - IF Synthesizer Fixed Frequency Selection (R2[6:5])
The IF_FREQ control word is used to set the default fixed IF frequency applicable to the specific CDMA system. For LMX2542,
the default fixed IF frequency is 367.20 MHz.
2.4.4 OSC_FREQ - Reference Oscillator Frequency Select (R2[7])
The OSC_FREQ bit is used to select the appropriate reference oscillator frequency.
MSB
23
1
22
1
OSC_FREQ
Control Bit
Control Bit
IF_EN
21
0
0
0
1
1
0
0
1
20
0
19
1
IF_CUR[1:0]
18
Register Location
Register Location
IF_FREQ[1:0]
0
17
0
R2[2]
R2[7]
16
1
15
0
SHIFT REGISTER BIT LOCATION
14
0
1
0
1
(Continued)
0
IF Synthesizer
Enable
Reference Oscillator
Select
DATA[21:0] FIELD
0
1
0
13
Description
Description
0
12
19
0
11
0
10
0
IF Synthesizer
Powered Down
19.20 MHz
Reference Oscillator
Selected
VCO_CUR
9
[1:0]
8
Charge Pump Current Gain
0
0
FREQ
OSC_
7
IF Synthesizer
Fixed IF Frequency
Function
Function
IF_FREQ
6
[1:0]
(µA)
100
200
300
800
170.76
367.20
440.76
(MHz)
IF Synthesizer Active
19.68 MHz
Reference Oscillator
Selected
5
IF_CUR
4
[1:0]
1
1
3
IF_
EN
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2
ADDRESS
1
1
FIELD
[1:0]
LSB
0
0