SNVS443C May   2006  – December 2016 LM3489 , LM3489-Q1

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: LM3489
    3. 6.3 ESD Ratings: LM3489-Q1
    4. 6.4 Recommended Operating Conditions
    5. 6.5 Thermal Information
    6. 6.6 Electrical Characteristics
    7. 6.7 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Hysteretic Control Circuit
        1. 7.3.1.1 Delay
      2. 7.3.2 Current Limit Operation
      3. 7.3.3 Start Up
      4. 7.3.4 External Sense Resistor
      5. 7.3.5 PGATE
      6. 7.3.6 Adjustable UVLO
    4. 7.4 Device Functional Mode
      1. 7.4.1 Device Enable and Shutdown
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Inductor Selection (L)
        2. 8.2.2.2 Output Capacitor Selection (COUT)
        3. 8.2.2.3 Input Capacitor Selection (CIN)
        4. 8.2.2.4 Programming the Current Limit (RADJ)
        5. 8.2.2.5 Catch Diode Selection (D1)
        6. 8.2.2.6 P-Channel MOSFET Selection (Q1)
        7. 8.2.2.7 Interfacing With the Enable Pin
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Examples
  11. 11Device and Documentation Support
    1. 11.1 Related Links
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

9 Power Supply Recommendations

This device is designed to operate over a recommended input voltage supply range of 4.5 V to 35 V. The input supply must be well regulated. If the input supply is located far from the LM3485 EVM and needs a long power supply cable to connect, an additional bulk capacitor may be required. An electrolytic capacitor with a value of
47 µF can be used typically.

As mentioned in Current Limit Operation, at higher input voltages (> 28 V) an increased negative SW transient spike at the switch node can lead to an increase in the current limit threshold due to the formation of the parasitic NPN connection between the ISENSE pin, the internal substrate and the ADJ pin . To avoid this issue, a Schottky catch diode with lower forward voltage drop must be used. In addition to that, a resistor must be placed between the ISENSE pin and the external switch node. A resistor value in the range of 220 Ω to 600 Ω is recommended.