SLVSEI2A November   2018  – May 2019 TPS56339

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
      2.      TPS56339 Efficiency
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin 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 Timing Requirements
    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 Advanced Emulated Current Mode Control
      2. 7.3.2 Enable and Adjusting Undervoltage Lockout
      3. 7.3.3 Soft Start and Pre-Biased Soft Start
      4. 7.3.4 Voltage Reference
      5. 7.3.5 Minimum ON-time, Minimum OFF-time and Frequency Foldback at Dropout Conditions
      6. 7.3.6 Overcurrent and Undervoltage Protection
      7. 7.3.7 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Active Mode
      3. 7.4.3 CCM Operation
    5. 7.5 Light-Load Operation
  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 Custom Design With WEBENCH® Tools
        2. 8.2.2.2 Output Voltage Resistors Selection
        3. 8.2.2.3 Output Inductor Selection
        4. 8.2.2.4 Output Capacitor Selection
        5. 8.2.2.5 Input Capacitor Selection
        6. 8.2.2.6 Bootstrap Capacitor Selection
      3. 8.2.3 Undervoltage Lockout Set Point
      4. 8.2.4 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Receiving Notification of Documentation Updates
    2. 11.2 Related Links
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

7.3.6 Overcurrent and Undervoltage Protection

The TPS56339 is protected from overcurrent conditions by cycle-by-cycle current limiting on both the peak and valley of the inductor current.

During the on time of the high-side MOSFET switch, the inductor current flow through high-side FET and increases at a linear rate determined by VIN, VOUT, the on-time and the output inductor value. The high-side switch current is sensed when the high-side is turned on after a set blanking time and then compared with the high-side MOSFET current limit every switching cycle. If the cross-limit event detected after the minimum On-time, the high-side MOSFET is turned off immediately and the high-side MOSFET current is limited by a clamped maximum peak current threshold IHS_LIMIT which is constant.

The current going through low-side MOSFET is also sensed and monitored. When the low-side MOSFET turns on, the inductor current begins to ramp down. The low-side MOSFET is not turned OFF at the end of a switching cycle if its current is above the low-side current limit ILS_LIMIT. The low-side MOSFET is kept ON for the next cycle so that inductor current keeps ramping down, until the inductor current ramps below the low-side current limit ILS_LIMIT and the subsequent switching cycle comes, the low-side MOSFET is turned OFF, and the high-side MOSFET is turned on after a dead time.

There are some important considerations for this type of overcurrent protection. The load current is higher than the overcurrent threshold by one half of the peak-to-peak inductor ripple current. Also, when the current is being limited, the output voltage tends to fall as the demanded load current may be higher than the current available from the converter. When the VFB voltage falls below the UVP threshold voltage, the UVP comparator detects it. The device will shut down after the UVP delay time (typically 120 μs) and re-start after the hiccup time (typically 38 ms). The hiccup mode helps to reduce the device power dissipation under severe overcurrent conditions.

When the over current condition is removed, the output voltage returns to the regulated value.