SNAS236G October   2005  – January 2016 LMX2485 , LMX2485E

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Timing Requirements
    7. 6.7 Typical Characteristics
      1. 6.7.1 Sensitivity
      2. 6.7.2 FinRF Input Impedance
      3. 6.7.3 FinIF Input Impedance
      4. 6.7.4 OSCin Input Impedance
      5. 6.7.5 Currents
  7. 7 Parameter Measurement Information
    1. 7.1 Bench Test Set-Ups
      1. 7.1.1 Charge Pump Current Measurement
      2. 7.1.2 Charge Pump Current Specification Definitions
        1. 7.1.2.1 Charge Pump Output Current Magnitude Variation vs Charge Pump Output Voltage
        2. 7.1.2.2 Charge Pump Sink Current vs Charge Pump Output Source Current Mismatch
        3. 7.1.2.3 Charge Pump Output Current Magnitude Variation vs Temperature
      3. 7.1.3 Sensitivity Measurement Procedure
      4. 7.1.4 Input Impedance Measurement
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 TCXO, Oscillator Buffer, and R Counter
      2. 8.3.2 Phase Detector
      3. 8.3.3 Charge Pump
      4. 8.3.4 Loop Filter
      5. 8.3.5 N Counters and High Frequency Input Pins
        1. 8.3.5.1 High Frequency Input Pins, FinRF and FinIF
        2. 8.3.5.2 Complementary High Frequency Pin, FinRF*
      6. 8.3.6 Digital Lock Detect Operation
      7. 8.3.7 Cycle Slip Reduction and Fastlock
        1. 8.3.7.1 Cycle Slip Reduction (CSR)
        2. 8.3.7.2 Fastlock
        3. 8.3.7.3 Using Cycle Slip Reduction (CSR) to Avoid Cycle Slipping
          1. 8.3.7.3.1 (Fastlock Charge Pump Current) / (Steady-State Charge Pump Current) = CSR
        4. 8.3.7.4 Using Fastlock to Improve Lock Times
        5. 8.3.7.5 Capacitor Dielectric Considerations for Lock Time
      8. 8.3.8 Fractional Spur and Phase Noise Controls
    4. 8.4 Device Functional Modes
      1. 8.4.1 Power Pins, Power-Down, and Power-Up Modes
    5. 8.5 Programming
      1. 8.5.1 General Programming Information
        1. 8.5.1.1 Register Location Truth Table
        2. 8.5.1.2 Control Register Content Map
        3. 8.5.1.3 Quick Start Register Map
        4. 8.5.1.4 Complete Register Map
    6. 8.6 Register Maps
      1. 8.6.1 R0 Register
        1. 8.6.1.1 RF_FN[11:0]—Fractional Numerator for RF PLL
        2. 8.6.1.2 RF_N[10:0]—RF N Counter Value
      2. 8.6.2 R1 Register
        1. 8.6.2.1 RF_FD[11:0]—RF PLL Fractional Denominator
        2. 8.6.2.2 RF_R [5:0]—RF R Divider Value
        3. 8.6.2.3 RF_P—RF Prescaler Bit
        4. 8.6.2.4 RF_PD—RF Power-Down Control Bit
      3. 8.6.3 R2 Register
        1. 8.6.3.1 IF_N[18:0]—IF N Divider Value
        2. 8.6.3.2 IF_PD—IF Power Down Bit
      4. 8.6.4 R3 Register
        1. 8.6.4.1 IF_R[11:0]—IF R Divider Value
        2. 8.6.4.2 RF_CPG—RF PLL Charge Pump Gain
        3. 8.6.4.3 ACCESS—Register Access Word
      5. 8.6.5 R4 Register
        1. 8.6.5.1 MUX[3:0] Frequency Out and Lock Detect MUX
        2. 8.6.5.2 IF_P—IF Prescaler
        3. 8.6.5.3 RF_CPP—RF PLL Charge Pump Polarity
        4. 8.6.5.4 IF_CPP—IF PLL Charge Pump Polarity
        5. 8.6.5.5 OSC_OUT Oscillator Output Buffer Enable
        6. 8.6.5.6 OSC2X—Oscillator Doubler Enable
        7. 8.6.5.7 FM[1:0]—Fractional Mode
        8. 8.6.5.8 DITH[1:0]—Dithering Control
        9. 8.6.5.9 ATPU—PLL Automatic Power Up
      6. 8.6.6 R5 Register
        1. 8.6.6.1 Fractional Numerator Determination [ RF_FN[21:12], RF_FN[11:0], Access[1] ]
        2. 8.6.6.2 Fractional Denominator Determination [ RF_FD[21:12], RF_FD[11:0], Access[1]]
      7. 8.6.7 R6 Register
        1. 8.6.7.1 RF_TOC—RF Time Out Counter and Control for FLoutRF Pin
        2. 8.6.7.2 RF_CPF—RF PLL Fastlock Charge Pump Current
        3. 8.6.7.3 CSR[1:0]—RF Cycle Slip Reduction
      8. 8.6.8 R7 Register
        1. 8.6.8.1 DIV4—RF Digital Lock Detect Divide By 4
        2. 8.6.8.2 IF_RST—IF PLL Counter Reset
        3. 8.6.8.3 RF_RST—RF PLL Counter Reset
        4. 8.6.8.4 RF_TRI—RF Charge Pump Tri-State
        5. 8.6.8.5 IF_TRI—IF Charge Pump Tri-State
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Related Links
    2. 12.2 Community Resources
    3. 12.3 Trademarks
    4. 12.4 Electrostatic Discharge Caution
    5. 12.5 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

9.1 Application Information

This device ideal for use in a broad class of applications, especially those requiring low current consumption and low fractional spurs. For applications that only need a single PLL, the unused PLL can be powered down and will not draw any extra current or generate any spurs or crosstalk.

9.2 Typical Application

LMX2485 LMX2485E sch_apps_snas236.gif Figure 24. Typical Application With Just RF Side Used

9.2.1 Design Requirements

Table 50 lists the design parameters of the LMX2485x.

Table 50. Design Parameters

PARAMETER VALUE
PM Phase Margin 48.3 degrees
BW Loop Bandwidth 11.3 kHz
T3/T1 Pole Ratios 40.20%
T4/T3 36.30%
KPD Phase Detector Gain 400 µA
fPD Phase Detector Frequency 10 MHz
fVCO Output Frequency 2400 – 2480 MHz
Vcc Supply Voltage 3 V
KVCO VCO Gain 55 MHz/V
CVCO VCO Input Capacitance 22 pF
C1_LF Loop Filter Components 2.7 nF
C2_LF 47 nF
C3_LF 270 pF
C4_LF 180 pF
R2_LF 820 Ω
R3_LF 3.9 kΩ
R4_LF 5.6 kΩ

9.2.2 Detailed Design Procedure

The design of the loop filter involves balancing requirements of lock time, spurs, and phase noise. This design is fairly involved, but the TI website has references, design tools, and simulation tools cover the loop filter design and simulation in depth.

9.2.3 Application Curves

LMX2485 LMX2485E ta_pn1_snas236.gif Figure 25. Phase Noise at 2440 MHz
LMX2485 LMX2485E ta_pn2_snas236.gif Figure 26. Spurs for Fractional Channel of 2440.2 MHz