SBVS360A February   2020  – November 2020 TPS7B85-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
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Switching 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 Enable (EN)
      2. 7.3.2 Power-Good (PG)
        1. 7.3.2.1 Adjustable Power-Good (PGADJ)
      3. 7.3.3 Adjustable Power-Good Delay Timer (DELAY)
      4. 7.3.4 Sense Comparator
      5. 7.3.5 Undervoltage Lockout
      6. 7.3.6 Thermal Shutdown
      7. 7.3.7 Current Limit
    4. 7.4 Device Functional Modes
      1. 7.4.1 Device Functional Mode Comparison
      2. 7.4.2 Normal Operation
      3. 7.4.3 Dropout Operation
      4. 7.4.4 Disabled
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Input and Output Capacitor Selection
      2. 8.1.2 Dropout Voltage
      3. 8.1.3 Reverse Current
      4. 8.1.4 Power Dissipation (PD)
        1. 8.1.4.1 Thermal Performance Versus Copper Area
      5. 8.1.5 Estimating Junction Temperature
      6. 8.1.6 SI Pin
        1. 8.1.6.1 Calculating the Sense Input (SI) Pin Threshold
        2. 8.1.6.2 Different Uses for the Sense Input Pin
          1. 8.1.6.2.1 Monitoring Input Voltage
          2. 8.1.6.2.2 Creating OV and UV Power-Good
          3. 8.1.6.2.3 Monitoring a Separate Supply Voltage
      7. 8.1.7 Pulling Up the SO and PG Pins to a Different Voltage
      8. 8.1.8 Power-Good
        1. 8.1.8.1 Setting the Adjustable Power-Good Threshold
        2. 8.1.8.2 Setting the Adjustable Power-Good Delay
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Input Capacitor
        2. 8.2.2.2 Output Capacitor
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Package Mounting
      2. 10.1.2 Board Layout Recommendations to Improve PSRR and Noise Performance
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Device Nomenclature
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Support Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary

7.4.3 Dropout Operation

If the input voltage is lower than the nominal output voltage plus the specified dropout voltage, but all other conditions are met for normal operation, the device operates in dropout mode. In this mode, the output voltage tracks the input voltage. During this mode, the transient performance of the device becomes significantly degraded because the pass transistor is in the ohmic or triode region, and acts as a switch. Line or load transients in dropout can result in large output-voltage deviations.

When the device is in a steady dropout state (defined as when the device is in dropout, VIN < VOUT(NOM) + VDO, directly after being in a normal regulation state, but not during startup), the pass transistor is driven into the ohmic or triode region. When the input voltage returns to a value greater than or equal to the nominal output voltage plus the dropout voltage (VOUT(NOM) + VDO), the output voltage can overshoot for a short period of time while the device pulls the pass transistor back into the linear region.