SLVSD88M July   2016  – August 2026 TPS61099

PRODMIX  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison Table
  6. 5 Pin Configuration and Functions
  7. 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
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Boost Controller Operation
      2. 7.3.2 Undervoltage Lockout
      3. 7.3.3 Enable and Disable
      4. 7.3.4 Soft Start
      5. 7.3.5 Current Limit Operation
      6. 7.3.6 Output Short-to-Ground Protection
      7. 7.3.7 Overvoltage Protection
      8. 7.3.8 Down Mode Regulation and Pass-Through Operation
      9. 7.3.9 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Burst Mode Operation under Light Load Condition
      2. 7.4.2 Down Mode Regulation and Pass-Through Mode Operation
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application - 5V Output Boost Converter
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Custom Design With WEBENCH® Tools
        2. 8.2.2.2 Programming the Output Voltage
        3. 8.2.2.3 Maximum Output Current
        4. 8.2.2.4 Inductor Selection
        5. 8.2.2.5 Capacitor Selection
      3. 8.2.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Third-Party Products Disclaimer
      2. 9.1.2 Development Support
        1. 9.1.2.1 Custom Design With WEBENCH® Tools
    2. 9.2 Documentation Support
      1. 9.2.1 Related Documentation
    3. 9.3 Receiving Notification of Documentation Updates
    4. 9.4 Support Resources
    5. 9.5 Trademarks
    6. 9.6 Electrostatic Discharge Caution
    7. 9.7 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

7.3.8 Down Mode Regulation and Pass-Through Operation

The TPS61099x features down mode and pass-through operation when input voltage is close to or higher than output voltage.

In the down mode, output voltage is regulated at target value even when VIN > VOUT. The control circuit changes the behavior of the rectifying PMOS by pulling the gate to input voltage instead of to ground. In this way, the voltage drop across the PMOS is increasing as high as to regulate the output voltage. The power loss also increases in this mode, which needs to be taken into account for thermal consideration.

In the Pass-Through operation, the boost converter stops switching. The rectifying PMOS constantly turns on and low side switch constantly turns off. The output voltage is the input voltage minus the voltage drop across the dc resistance (DCR) of the inductor and the on-resistance of the rectifying PMOS.

With VIN ramping up, the TPS61099x goes into down mode first when VIN > VOUT – 50mV. TPS61099x stays in down mode until VIN > VOUT + 0.5V and then goes automatically into pass-through operation. In the pass-through operation, output voltage follows input voltage. The TPS61099x exits pass-through mode and goes back to down mode when VIN ramps down to 103% of the target output voltage. TPS61099x stays in down mode until input voltage falls 100mV below the output voltage, returning to boost operation.

TPS61099 Down Mode and Pass-Through OperationFigure 7-3 Down Mode and Pass-Through Operation