SNVS178H January   2002  – December 2015 LM3485

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 Electrical Characteristics
    6. 6.6 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
      2. 7.3.2 Current Limit Operation
    4. 7.4 Device Functional Modes
      1. 7.4.1 Start Up
      2. 7.4.2 External Sense Resistor
      3. 7.4.3 PGATE
  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 Step by Step Design Procedure
        2. 8.2.2.2 Inductor Selection (L1)
        3. 8.2.2.3 Output Voltage Set Point
        4. 8.2.2.4 Output Capacitor Selection (COUT)
        5. 8.2.2.5 Input Capacitor Selection (CIN)
        6. 8.2.2.6 Programming the Current Limit (RADJ)
        7. 8.2.2.7 Catch Diode Selection (D1)
        8. 8.2.2.8 P-Channel MOSFET Selection (Q1)
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
    2. 11.2 Community Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

1 Features

  • Easy-to-Use Control Methodology
  • No Control-Loop Compensation Required
  • 4.5-V to 35-V Wide Input Range
  • 1.242-V to VIN Adjustable Output Range
  • High Efficiency 93%
  • ±1.3% (±2% Over Temp) Internal Reference
  • 100% Duty Cycle
  • Maximum Operating Frequency > 1 MHz
  • Current Limit Protection

2 Applications

  • Set-Top Box
  • DSL or Cable Modem
  • PC/IA
  • Auto PC
  • TFT Monitor
  • Battery-Powered Portable Applications
  • Distributed Power Systems
  • Always On Power

3 Description

The LM3485 is a high-efficiency PFET switching regulator controller that can be used to quickly and easily develop a small, low-cost, switching buck regulator for a wide range of applications. The hysteretic control architecture provides for simple design without any control-loop stability concerns using a wide variety of external components. The PFET architecture also allows for low component count as well as ultralow dropout, 100% duty cycle operation. Another benefit is high efficiency operation at light loads without an increase in output ripple.

Current limit protection is provided by measuring the voltage across the RDS(ON) of the PFET, thus eliminating the need for a sense resistor. The cycle-by-cycle current limit can be adjusted with a single resistor, ensuring safe operation over a range of output currents.

Device Information(1)

PART NUMBER PACKAGE BODY SIZE (NOM)
LM3485 VSSOP (8) 3.0 mm × 3.0 mm
  1. For all available packages, see the orderable addendum at the end of the data sheet.

Typical Application Circuit

LM3485 20034608.png