LMX2582 Datasheet, PDF (30/40 Pages) Texas Instruments – High Performance, Wideband PLLatinum RF Synthesizer

LMX2582
SNAS680A – DECEMBER 2015 – REVISED DECEMBER 2015
www.ti.com
Figure 28. Moving Away from Fvco % Fpd Spur
8.1.5.2 Multiplying and Dividing by the Same Value
Although it may not seem like the first thing to try, the Fvco%Fosc and Fout%Fosc spur can sometimes be
improved engaging the OSC_2X bit and then dividing by 2. Although this gives the same phase detector
frequency, the spur can be improved.
8.1.6 Designing for Output Power
If there is a desired frequency for highest power, use an inductor pull-up and design for the value so that the
resonance is at that frequency. Use the formula SRF = 1 / (2π× sqrt[L × C]).
Example: C = 1.4 pF (characteristic). If max power is targeted at 1 GHz, L = 18 nH. If max power is targeted at
3.3 GHz, L = 1.6 nH
25
1.6 nH pull-up
20
18 nH pull-up
50 : pull-up
15
10
5
0
-5
-10
100
200
500
1000 2000 5000
D023
Figure 29. Output Power Versus Pull-Up Type
8.1.7 Current Consumption Management
The starting point is the typical total current consumption of 250 mA: 100-MHz input frequency, OSCin doubler
bypassed, Pre-R divider bypassed, multiplier bypassed, post-R divider bypassed, 100-MHz phase detector
frequency, 0.468-mA charge pump current, channel divider off, one output on, 5400-MHz output frequency, 50-Ω
output pull-up, 0-dBm output power (differential). To understand current consumption changes due to engaging
different fuctional blocks , refer to Table 42.
ACTION
Use input signal path
Table 42. Typical Current Consumption Impact By Function
STEPS
Enable OSCin doubler
Enable multiplier
PROGRAMMING
OSC_2X = 1
MULT = 3,4,5, or 6
INCREASE IN CURRENT (mA)
7
10
30
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