LMX2485E (ACTIVE)

Delta-Sigma Low Power Dual PLL for RF Personal Communications

 

Description

The LMX2485 device is a low power, high performance delta-sigma fractional-N PLL with an auxiliary integer-N PLL. The device is fabricated using Texas Instruments’ advanced process.

With delta-sigma architecture, fractional spurs at lower offset frequencies are pushed to higher frequencies outside the loop bandwidth. The ability to push close in spur and phase noise energy to higher frequencies is a direct function of the modulator order. Unlike analog compensation, the digital feedback technique used in the LMX2485 is highly resistant to changes in temperature and variations in wafer processing. The LMX2485 delta-sigma modulator is programmable up to fourth order, which allows the designer to select the optimum modulator order to fit the phase noise, spur, and lock time requirements of the system.

Serial data for programming the LMX2485 is transferred through a three-line, high-speed (20-MHz) MICROWIRE interface. The LMX2485 offers fine frequency resolution, low spurs, fast programming speed, and a single-word write to change the frequency. This makes it ideal for direct digital modulation applications, where the N-counter is directly modulated with information. The LMX2485 is available in a 24-lead 4.0 × 4.0 × 0.8 mm WQFN package.

Features

  • Quadruple Modulus Prescaler for Lower Divides
    • RF PLL: 8/9/12/13 or 16/17/20/21
    • IF PLL: 8/9 or 16/17
  • Advanced Delta-Sigma Fractional Compensation
    • 12-Bit or 22-Bit Selectable Fractional Modulus
    • Up to 4th Order Programmable Delta-Sigma
      Modulator
  • Features for Improved Lock Time
    • Fastlock / Cycle Slip Reduction With Integrated
      Time-Out Counter Which Requires Only a
      Single-Word Write
  • Wide Operating Range
    • LMX2485 RF PLL: 500 MHz to 3.0 GHz
    • LMX2485E RF PLL: 50 MHz to 3.0 GHz
  • Useful Features
    • Digital Lock Detect Output
    • Hardware and Software Power-Down Control
    • On-Chip Input Frequency Doubler.
    • RF Phase Detector Frequency up to 50 MHz
    • 2.5 to 3.6 V Operation With ICC = 5.0 mA

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Parametrics Compare all products in RF PLLs and Synthesizers

 
Output Frequency (Min) (MHz)
Output Frequency (Max) (MHz)
Normalized PLL Phase Noise (dBc/Hz)
VCO Phase Noise (Nom) (dBc/Hz)
1/f Noise (10 kHz offset at 1 GHz carrier) (dBc/Hz)
Current Consumption (mA)
VCC (V)
Integrated VCO
Pin/Package
LMX2485E LMX2485Q-Q1 LMX2486 LMX2487 LMX2487E LMX2491 LMX2492 LMX2571 LMX2581
50    500    1000    1000    3000    500    500    10    50   
3000    3100    4500    6000    7500    6400    14000    1344    3760   
-210    -210    -210    -210    -210    -227    -227    -231    -229   
N/A    N/A    N/A    N/A    N/A    N/A    N/A    -115    -121   
-104    -104    -104    -104    -104    -120    -120    -124    -125   
3.3    3.3    5.7    5.7    5.7    60    60    39    178   
2.5 to 3.6    2.5 to 3.6    2.5 to 3.6    2.5 to 3.6    2.5 to 3.6    3.15 to 3.45    3.15 to 3.45    3.15 to 5    3.15 to 3.45   
No    No    No    No    No    No    No    Yes    Yes   
24WQFN    24WQFN    24WQFN    24WQFN    24WQFN    24WQFN    24WQFN      32WQFN   

Featured tools and software

WEBENCH® Designer LMX2485E

Recommend Input Frequency Tunable Output Frequency
   
Input Frequency Min Output Frequency
 MHz  MHz
 
Max Output Frequency
 MHz
Channel Spacing
 MHz