SBAS486F November   2009  – February 2016 ADS41B29 , ADS41B49

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: General
    6. 6.6  Electrical Characteristics: ADS41B29, ADS41B49
    7. 6.7  Digital Characteristics
    8. 6.8  Timing Requirements: LVDS and CMOS Modes
    9. 6.9  Timing Requirements: Reset
    10. 6.10 Timing Requirements: LVDS Timing Across Sampling Frequencies
    11. 6.11 Timing Requirements: CMOS Timing Across Sampling Frequencies
    12. 6.12 Timing Requirements: CMOS Timing Across Sampling Frequencies
    13. 6.13 Typical Characteristics: ADS41B49
    14. 6.14 Typical Characteristics: ADS41B29
    15. 6.15 Typical Characteristics: General
    16. 6.16 Typical Characteristics: Contour
  7. 7 Parameter Measurement Information
    1. 7.1 Timing Diagrams
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Analog Input
      2. 8.3.2 Clock Input
      3. 8.3.3 Gain for SFDR, SNR Trade-Off
      4. 8.3.4 Offset Correction
      5. 8.3.5 Digital Output Information
        1. 8.3.5.1 Output Interface
        2. 8.3.5.2 DDR LVDS Outputs
        3. 8.3.5.3 LVDS Output Data and Clock Buffers
        4. 8.3.5.4 Parallel CMOS Interface
        5. 8.3.5.5 CMOS Interface Power Dissipation
        6. 8.3.5.6 Input Overvoltage Indication (OVR Pin)
        7. 8.3.5.7 Output Data Format
    4. 8.4 Device Functional Modes
      1. 8.4.1 Device Configuration
      2. 8.4.2 Power-Down
        1. 8.4.2.1 Power-Down Global
        2. 8.4.2.2 Standby
        3. 8.4.2.3 Output Buffer Disable
        4. 8.4.2.4 Input Clock Stop
    5. 8.5 Programming
      1. 8.5.1 Serial Interface
        1. 8.5.1.1 Register Initialization
      2. 8.5.2 Serial Register Readout
    6. 8.6 Register Maps
      1. 8.6.1 Serial Register Map
        1. 8.6.1.1 Summary of High-Performance Modes
        2. 8.6.1.2 Description of Serial Registers
          1. 8.6.1.2.1  Register Address 00h (address = 00h) [reset = 00h]
          2. 8.6.1.2.2  Register Address 01h (address = 01h) [reset = 00h]
          3. 8.6.1.2.3  Register Address 03h (address = 03h) [reset = 00h]
          4. 8.6.1.2.4  Register Address 25h (address = 25h) [reset = 50h]
          5. 8.6.1.2.5  Register Address 26h (address = 26h) [reset = 00h]
          6. 8.6.1.2.6  Register Address 3Dh (address = 3Dh) [reset = 00h]
          7. 8.6.1.2.7  Register Address 3Fh (address = 3Fh) [reset = 00h]
          8. 8.6.1.2.8  Register Address 40h (address = 40h) [reset = 00h]
          9. 8.6.1.2.9  Register Address 41h (address = 41h) [reset = 00h]
          10. 8.6.1.2.10 Register Address 42h (address = 42h) [reset = 08h]
          11. 8.6.1.2.11 Register Address 43h (address = 43h) [reset = 00h]
          12. 8.6.1.2.12 Register Address 4Ah (address = 4Ah) [reset = 00h]
          13. 8.6.1.2.13 Register Address BFh (address = BFh) [reset = 00h]
          14. 8.6.1.2.14 Register Address CFh (address = CFh) [reset = 00h]
          15. 8.6.1.2.15 Register Address DFh (address = DFh) [reset = 00h]
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Drive Circuit Requirements
      2. 9.1.2 Driving Circuit
  10. 10Power Supply Recommendations
    1. 10.1 Power-Supply Sequence
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 Board Design Considerations
        1. 11.1.1.1 Grounding
        2. 11.1.1.2 Supply Decoupling
        3. 11.1.1.3 Exposed Pad
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Related Links
    3. 12.3 Community Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and 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

9.1.1 Drive Circuit Requirements

For optimum performance, the analog inputs must be driven differentially. This technique improves the common-mode noise immunity and even-order harmonic rejection. A small resistor (5 Ω to 10 Ω) in series with each input pin is recommended to damp out ringing caused by package parasitics.

Figure 83 and Figure 84 show the differential impedance (ZIN = RIN || CIN) between the ADC analog input pins INP and INM. The presence of the analog input buffer results in an almost constant input capacitance up to 1 GHz.

ADS41B29 ADS41B49 ai_rin-frq_bas486.gif Figure 83. ADC Analog Input Resistance (RIN) Across Frequency
ADS41B29 ADS41B49 ai_cin-frq_bas486.gif Figure 84. ADC Analog Input Capacitance (CIN) Across Frequency

9.1.2 Driving Circuit

Two example driving circuit configurations are shown in Figure 85 and Figure 86—one optimized for low input frequencies and the other optimized for high input frequencies. Notice in both cases that the board circuitry is simplified compared to the non-buffered ADS4149.

In Figure 85, a single transformer is used and is suited for low input frequencies. To optimize even-harmonic performance at high input frequencies (greater than the first Nyquist), the use of back-to-back transformers is recommended (see Figure 86). Note that both drive circuits have been terminated by 50 Ω near the ADC side. The ac-coupling capacitors allow the analog inputs to self-bias around the required common-mode voltage.

ADS41B29 ADS41B49 ai_drvr_lo_bas487.gif Figure 85. Drive Circuit for Low Input Frequencies
ADS41B29 ADS41B49 ai_drvr_hi_bas487.gif Figure 86. Drive Circuit for High Input Frequencies

The mismatch in the transformer parasitic capacitance (between the windings) results in degraded even-order harmonic performance. Connecting two identical RF transformers back-to-back helps minimize this mismatch and good performance is obtained for high-frequency input signals. An additional termination resistor pair may be required between the two transformers, as shown in Figure 85 and Figure 86. The center point of this termination is connected to ground to improve the balance between the P (positive) and M (negative) sides. The values of the terminations between the transformers and on the secondary side must be chosen to obtain an effective 50 Ω (for a 50-Ω source impedance).