SNVS037H September   1999  – March 2024 LM1084

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Ripple Rejection
      2. 6.3.2 Load Regulation
      3. 6.3.3 Overload Recovery
    4. 6.4 Device Functional Modes
      1. 6.4.1 Output Voltage
      2. 6.4.2 Stability Consideration
      3. 6.4.3 Protection Diodes
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Applications
      1. 7.2.1  1.2-V to 15-V Adjustable Regulator
        1. 7.2.1.1 Design Requirements
        2. 7.2.1.2 Detailed Design Procedure
        3. 7.2.1.3 Application Curve
      2. 7.2.2  Adjustable at 5 V
      3. 7.2.3  5-V Regulator With Shutdown
      4. 7.2.4  Battery Charger
      5. 7.2.5  Adjustable Fixed Regulator
      6. 7.2.6  Regulator with Reference
      7. 7.2.7  High Current Lamp Driver Protection
      8. 7.2.8  Battery Backup Regulated Supply
      9. 7.2.9  Ripple Rejection Enhancement
      10. 7.2.10 Automatic Light Control
      11. 7.2.11 Generating Negative Supply Voltage
      12. 7.2.12 Remote Sensing
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
        1. 7.4.1.1 Thermal Considerations
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Receiving Notification of Documentation Updates
    2. 8.2 Support Resources
    3. 8.3 Trademarks
    4. 8.4 Electrostatic Discharge Caution
    5. 8.5 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

Package Options

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

6.3.1 Ripple Rejection

Ripple rejection is a function of the open loop gain within the feed-back loop (refer to Figure 6-1 and Figure 6-4). The LM1084 exhibits 75dB of ripple rejection (typ.). When adjusted for voltages higher than VREF, the ripple rejection decreases as a function of adjustment gain: (1+R1/R2) or VO/VREF. Therefore a 5-V adjustment decreases ripple rejection by a factor of four (−12dB); Output ripple increases as adjustment voltage increases.

However, the adjustable version allows this degradation of ripple rejection to be compensated. The adjust terminal can be bypassed to ground with a capacitor (CADJ). The impedance of the CADJ should be equal to or less than R1 at the desired ripple frequency. This bypass capacitor prevents ripple from being amplified as the output voltage is increased.

Equation 1. 1/(2π × fRIPPLE*CADJ) ≤ R1