SLVS537C June   2004  – May 2025 UA78M-Q1

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: UA78M33Q (Both Legacy and New Chip)
    6. 5.6 Electrical Characteristics: UA78M05Q (Both Legacy and New Chip)
    7. 5.7 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagrams
    3. 6.3 Feature Description
      1. 6.3.1 Current Limit
      2. 6.3.2 Dropout Voltage (VDO)
      3. 6.3.3 Thermal Shutdown
    4. 6.4 Device Functional Modes
      1. 6.4.1 Normal Operation
      2. 6.4.2 Dropout Operation
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1 Input and Output Capacitor Requirements
        2. 7.2.2.2 Power Dissipation (PD)
        3. 7.2.2.3 Estimating Junction Temperature
        4. 7.2.2.4 External Capacitor Requirements
        5. 7.2.2.5 Overload Recovery
        6. 7.2.2.6 Reverse Current
        7. 7.2.2.7 Polarity Reversal Protection
      3. 7.2.3 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Development Support
        1. 8.1.1.1 Evaluation Module
      2. 8.1.2 Device Nomenclature
    2. 8.2 Receiving Notification of Documentation Updates
    3. 8.3 Support Resources
    4. 8.4 Trademarks
    5. 8.5 Electrostatic Discharge Caution
    6. 8.6 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

7.2.2.5 Overload Recovery

Because the input voltage rises when power is first turned on, the output follows the input, allowing the regulator to start up into very heavy loads. The input-to-output voltage differential is small during start up when the input voltage is rising, allowing the regulator to supply large output currents. With a high input voltage, a problem occurs where removing an output short does not allow the output voltage to recover. Other regulators also exhibit this phenomenon, so the behavior is not unique to the UA78M-Q1.

The problem occurs with a heavy output load when the input voltage is high and the output voltage is low. Common situations occur immediately when removing a short circuit after the input voltage is already turned on. The load line for such a load potentially intersects the output current curve at two points. If this condition happens, there are two stable output operating points for the regulator. With this double intersection, the input power supply is potentially cycled down to zero. Bringing the power supply up again causes the output to recover to the desired voltage operating point.