SBOSA87A December   2021  – November 2022 LMH5485-SEP

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics: Vs+ – Vs- = 5 V
    6. 7.6 Electrical Characteristics: Vs+ – Vs- = 3 V
    7. 7.7 Typical Characteristics: 5 V Single Supply
    8. 7.8 Typical Characteristics: 3 V Single Supply
    9. 7.9 Typical Characteristics: 3 V to 5 V Supply Range
  8. 8 Parameter Measurement Information
    1. 8.1 Example Characterization Circuits
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Differential I/O
      2. 9.3.2 Power-Down Control Pin (PD)
        1. 9.3.2.1 Operating the Power Shutdown Feature
      3. 9.3.3 Input Overdrive Operation
    4. 9.4 Device Functional Modes
      1. 9.4.1 Operation from Single-Ended Sources to Differential Outputs
        1. 9.4.1.1 AC-Coupled Signal Path Considerations for Single-Ended Input to Differential Output Conversion
        2. 9.4.1.2 DC-Coupled Input Signal Path Considerations for Single-Ended to Differential Conversion
      2. 9.4.2 Differential-Input to Differential-Output Operation
        1. 9.4.2.1 AC-Coupled, Differential-Input to Differential-Output Design Issues
        2. 9.4.2.2 DC-Coupled, Differential-Input to Differential-Output Design Issues
  10. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Applications
      1. 10.2.1 Designing Attenuators
        1. 10.2.1.1 Design Requirements
        2. 10.2.1.2 Detailed Design Procedure
        3. 10.2.1.3 Application Curve
      2. 10.2.2 Interfacing to High-Performance ADCs
        1. 10.2.2.1 Design Requirements
        2. 10.2.2.2 Detailed Design Procedure
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
  13. 13Device and Documentation Support
    1. 13.1 Documentation Support
      1. 13.1.1 Related Documentation
    2. 13.2 Receiving Notification of Documentation Updates
    3. 13.3 Support Resources
    4. 13.4 Trademarks
    5. 13.5 Electrostatic Discharge Caution
    6. 13.6 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

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

9.4.1.1 AC-Coupled Signal Path Considerations for Single-Ended Input to Differential Output Conversion

When the signal path can be AC-coupled, the DC biasing for the LMH5485-SEP becomes a relatively simple task. In all designs, start by defining the output common-mode voltage. The AC-coupling issue can be separated for the input and output sides of an FDA design. In any case, the design starts by setting the desired VOCM. When an AC-coupled path follows the output pins, the best linearity is achieved by operating VOCM at mid-supply. The VOCM voltage must be within the linear range for the common-mode loop, as specified in the headroom specifications (approximately 0.91 V greater than the negative supply and 1.1 V less than the positive supply). If the output path is also AC coupled, simply letting the VOCM control pin float is usually preferred in order to get a mid-supply default VOCM bias with minimal elements. To limit noise, place a 0.1 µF decoupling capacitor on the VOCM pin to ground.

After VOCM is defined, check the target output voltage swing to ensure that the VOCM plus the positive or negative output swing on each side does not clip into the supplies. Check that VOCM ±Vp does not exceed the absolute supply rails for this rail-to-rail output (RRO) device.

Going to the device input pins side, because both the source and balancing resistor on the nonsignal input side are DC blocked (see Figure 8-1), no common-mode current flows from the output common-mode voltage, thus setting the input common-mode equal to the output common-mode voltage.

This input headroom also sets a limit for higher VOCM voltages. Because the input Vicm is the output VOCM for AC-coupled sources, the 1.2 V minimum headroom for the input pins to the positive supply overrides the 1.1 V headroom limit for the output VOCM. The input signal also moves this input Vicm around the DC bias point.