SNOSB30P October 2008  – January 2015 LMH6554

PRODUCTION DATA. 

  1. Features
  2. Applications
  3. Description
  4. Typical Application Schematic
  5. Revision History
  6. Pin Configuration and Functions
  7. Specifications
    1. 7.1Absolute Maximum Ratings
    2. 7.2ESD Ratings
    3. 7.3Recommended Operating Conditions
    4. 7.4Thermal Information
    5. 7.5Electrical Characteristics: +5 V
    6. 7.6Typical Performance Characteristics VS = ±2.5 V
  8. Detailed Description
    1. 8.1Overview
    2. 8.2Functional Block Diagram
    3. 8.3Feature Description
    4. 8.4Device Functional Modes
  9. Application and Implementation
    1. 9.1Application Information
    2. 9.2Typical Applications
      1. 9.2.1Single-Ended Input to Differential Output Operation
        1. 9.2.1.1Design Requirements
        2. 9.2.1.2Detailed Design Procedure
          1. 9.2.1.2.1Enable / Disable Operation
          2. 9.2.1.2.2Single-Ended Input to Differential Output Operation
          3. 9.2.1.2.3Driving Capacitive Loads
        3. 9.2.1.3Application Curves
      2. 9.2.2Fully Differential Operation
      3. 9.2.3Single Supply Operation
      4. 9.2.4Driving Analog-to-Digital Converters
      5. 9.2.5Output Noise Performance and Measurement
      6. 9.2.6Balanced Cable Driver
  10. 10Power Supply Recommendations
    1. 10.1Power Supply Bypassing
  11. 11Layout
    1. 11.1Layout Guidelines
    2. 11.2Layout Example
    3. 11.3Power Dissipation
    4. 11.4ESD Protection
  12. 12Device and Documentation Support
    1. 12.1Device Support
      1. 12.1.1Third-Party Products Disclaimer
    2. 12.2Documentation Support
      1. 12.2.1Related Documentation
    3. 12.3Trademarks
    4. 12.4Electrostatic Discharge Caution
    5. 12.5Glossary
  13. 13Mechanical, Packaging, and Orderable Information

11 Layout

11.1 Layout Guidelines

The LMH6554 is a high speed, high performance amplifier. In order to get maximum benefit from the differential circuit architecture board layout and component selection is very critical. The circuit board should have a low inductance ground plane and well bypassed broad supply lines. External components should be leadless surface mount types. The feedback network and output matching resistors should be composed of short traces and precision resistors (0.1%). The output matching resistors should be placed within 3 or 4 mm of the amplifier as should the supply bypass capacitors. Refer to Power Supply Bypassing for recommendations on bypass circuit layout. Evaluation boards are available through the product folder on ti.com.

By design, the LMH6554 is relatively insensitive to parasitic capacitance at its inputs. Nonetheless, ground and power plane metal should be removed from beneath the amplifier and from beneath RF and RG for best performance at high frequency.

With any differential signal path, symmetry is very important. Even small amounts of asymmetry can contribute to distortion and balance errors.

11.2 Layout Example

annot_top_nosb30.pngFigure 38. Layout Schematic

11.3 Power Dissipation

The LMH6554 is optimized for maximum speed and performance in a small form factor 14 lead UQFN package. To ensure maximum output drive and highest performance, thermal shutdown is not provided. Therefore, it is of utmost importance to make sure that the TJMAX is never exceeded due to the overall power dissipation.

Follow these steps to determine the maximum power dissipation for the LMH6554:

  1. Calculate the quiescent (no-load) power:
  2. Equation 1. PAMP = ICC * (VS)

    where

    • VS = V+ − V-. (Be sure to include any current through the feedback network if VCM is not mid-rail)
  3. Calculate the RMS power dissipated in each of the output stages:
  4. Equation 2. PD (rms) = rms ((VS − V+OUT) * I+OUT) + rms ((VS − V-OUT) * I-OUT)

    where

    • VOUT and IOUT are the voltage
    • the current measured at the output pins of the differential amplifier as if they were single ended amplifiers
    • VS is the total supply voltage
  5. Calculate the total RMS power:
  6. Equation 3. PT = PAMP + PD

The maximum power that the LMH6554 package can dissipate at a given temperature can be derived with the following equation:

Equation 4. PMAX = (150° − TAMB)/ θJA

where

  • TAMB = Ambient temperature (°C)
  • θJA = Thermal resistance, from junction to ambient, for a given package (°C/W)
  • For the 14 lead UQFN package, θJA is 60°C/W

NOTE

If VCM is not 0V then there will be quiescent current flowing in the feedback network. This current should be included in the thermal calculations and added into the quiescent power dissipation of the amplifier.

11.4 ESD Protection

The LMH6554 is protected against electrostatic discharge (ESD) on all pins. The LMH6554 can survive 2000 V Human Body model and 250 V Machine model events. Under normal operation the ESD diodes have no affect on circuit performance. There are occasions, however, when the ESD diodes will be evident. If the LMH6554 is driven by a large signal while the device is powered down the ESD diodes will conduct. The current that flows through the ESD diodes will either exit the chip through the supply pins or will flow through the device, hence it is possible to power up a chip with a large signal applied to the input pins. Using the shutdown mode is one way to conserve power and still prevent unexpected operation.