SNOSB28G August   2010  – November 2014 LMP8640 , LMP8640-Q1 , LMP8640HV

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Device Comparison Table
  6. Pin Configuration and Functions
  7. Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 Handling Ratings - LMP8640, LMP8640HV
    3. 7.3 Handling Ratings - LMP8640-Q1
    4. 7.4 Recommended Operating Conditions
    5. 7.5 Thermal Information
    6. 7.6 Electrical Characteristics 2.7 V
    7. 7.7 Electrical Characteristics 5 V
    8. 7.8 Electrical Characteristics 12 V
    9. 7.9 Typical Characteristics
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Selection of Sense Resistor
        1. 8.3.1.1 Resistor Power Rating and Thermal Issues
        2. 8.3.1.2 Using PCB Trace as a Sense Resistor
      2. 8.3.2 Sense Line Inputs
      3. 8.3.3 Effects of Series Resistance on Sense Lines
    4. 8.4 Device Functional Modes
      1. 8.4.1 Bias Current at Low Common Mode Voltage
      2. 8.4.2 Applying Input Voltage with No Supply Voltage
      3. 8.4.3 Driving an ADC
  9. Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Design Procedure
        1. 9.2.2.1 First Step - LMP8640 or LMP8640HV Selection
        2. 9.2.2.2 Second Step - Gain Option Selection
        3. 9.2.2.3 Third Step - Shunt Resistor Selection
      3. 9.2.3 Application Performance Plot
    3. 9.3 Do's and Don'ts Added Section
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Development Support
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
    3. 12.3 Related Links
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

11 Layout

11.1 Layout Guidelines

  • Use 4-wire (Kelvin) connections to the sense resistor. Connect to the resistor at a point that is not within a direct high-current path (See Figure 29).
  • Do not "share" part of the sense trace path with the load current.
  • Maintain proper clearance and spacings around the input traces, as they may be at a higher voltage (up to 76 V) than the surrounding traces and planes.
  • Input traces from the sense resistor pads should follow the same path, be spaced tightly together, and ideally on the same copper layer.
  • Vias used in the input traces should be of continuous plated copper to avoid creating thermocouples.
  • Avoid routing inputs through jumpers and connectors. Even the best connectors introduce thermal errors ("thermocouples"). Each input trace should have the same number of "thermocouples" if they cannot be avoided.
  • Keep the amplifier away from heat generating devices. The copper-solder-lead junction on the input pins will form a thermocouple. The copper mass should be equal on both input pins.
  • Avoid temperature gradients across the input pins. Input pins should be equal distance to the heat source.
  • Place the LMP8640 in the most temperature-stable area possible and away from high-velocity air flows. It is better to carefully extend the input traces than to place the amplifier in a less-than-ideal environment.
  • Give the sense resistor as much copper trace area as possible to dissipate heat as the resistor value will change slightly with temperature. Also see the resistor manufacturers datasheet or application notes for further layout guidelines.
  • The power-supply bypass capacitor should be placed as closely as possible to the supply and ground terminals. The recommended value of this bypass capacitor is 0.1 μF. Additional decoupling capacitance can be added to compensate for noisy or high-impedance power supplies.

11.2 Layout Example

Layout_3D.pngFigure 29. Layout Example - Kelvin Connection to a Two-Terminal Resistor
Layout_Kelvin_3D.pngFigure 30. Layout Example - Four-Wire (Kelvin) Resistor Connection