SNOSB29H November   2009  – May 2022 LMP8645 , LMP8645HV

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 2.7-V Electrical Characteristics
    6. 6.6 5-V Electrical Characteristics
    7. 6.7 12-V Electrical Characteristics
    8. 6.8 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
      1. 7.1.1 Theory of Operation
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Driving ADC
      2. 7.3.2 Applying Input Voltage With No Supply Voltage
    4. 7.4 Device Functional Modes
      1. 7.4.1 Selection of the Gain Resistor
      2. 7.4.2 Gain Range Limitations
        1. 7.4.2.1 Range 1: VCM is –2 V to 1.8 V
        2. 7.4.2.2 Range 2: VCM is 1.8 V to VS
        3. 7.4.2.3 Range 3: VCM is greater than VS
      3. 7.4.3 Selection of Sense Resistor
        1. 7.4.3.1 Resistor Power Rating and Thermal Issues
        2. 7.4.3.2 Using PCB Trace as a Sense Resistor
      4. 7.4.4 Sense Line Inputs
        1. 7.4.4.1 Effects of Series Resistance on Sense Lines
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Typical Current Monitor Application
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
        3. 8.2.1.3 Application Curves
      2. 8.2.2 High Brightness LED Driver
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Development Support
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Support Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

7.4.3.1 Resistor Power Rating and Thermal Issues

The power dissipated by the sense resistor can be calculated from:

Equation 7. PD = IMAX2 * RS

where

  • PD is the power dissipated by the resistor in Watts
  • IMAX is the maximum load current in A
  • RS is the sense resistor value in Ω.

The resistor must be rated for more than the expected maximum power (PD), with margin for temperature derating. Be sure to observe any power derating curves provided by the resistor manufacturer.

Running the resistor at higher temperatures will also affect the accuracy. As the resistor heats up, the resistance generally goes up, which will cause a change in the measurement. The sense resistor should have as much heat-sinking as possible to remove this heat through the use of heatsinks or large copper areas coupled to the resistor pads. A reading drifting slightly after turnon can usually be traced back to sense resistor heating.