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

8.2.1.2 Detailed Design Procedure

At the start-up of the monitored device, the LMP8645 works at a common-mode voltage of 0 V, which means that the maximum output limit is 1.3 V (Range 1). To maximize the resolution, the RSENSE value is calculated as maximum allowed VSENSE (Refer to Figure 7-3) divided by maximum current (1 A), so RSENSE=0.5 Ω.

Due to the output limitation at low common-mode voltage, the maximum allowed gain will be 2.6 V/V, which corresponds to RGAIN = 13 kΩ. With this approach the current is monitored correctly at any working condition, but does not use the full output swing range of the LMP8645.

Alternatively if the monitored device doesn’t sink the full 1 A at any supply voltage, it is possible to design with the full maximum output voltage of the LMP8645 when operating in Range 3 ( VCM ≥ VS ).

Also in this case it is possible to maximize the resolution using Rsense = 0.5 Ω, and maximize the output dynamic range with RGAIN=33 kΩ. With this approach the maximum detectable current, when VCM is less than 1.8 V, is about 400 mA. While for common-mode voltages of less than 2.5 V the maximum detectable current is 600 mA (Refer to Figure 7-3), and for common-mode voltages at or above the LMP8645 supply voltage, the maximum current is 1 A.

The second approach maximizes the output dynamic but implies some knowledge on the monitored current.