SLVSFQ0B October   2020  – June 2024 TPS54J061

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  Enable and Internal LDO
      2. 6.3.2  Split Rail and External LDO
      3. 6.3.3  Output Voltage Setting
      4. 6.3.4  Soft Start and Output-Voltage Tracking
      5. 6.3.5  Frequency and Operation Mode Selection
      6. 6.3.6  D-CAP3™ Control Mode
      7. 6.3.7  Current Sense and Positive Overcurrent Protection
      8. 6.3.8  Low-side FET Negative Current Limit
      9. 6.3.9  Power Good
      10. 6.3.10 Overvoltage and Undervoltage Protection
      11. 6.3.11 Out-Of-Bounds Operation (OOB)
      12. 6.3.12 Output Voltage Discharge
      13. 6.3.13 UVLO Protection
      14. 6.3.14 Thermal Shutdown
    4. 6.4 Device Functional Modes
      1. 6.4.1 Auto-Skip Eco-Mode Light Load Operation
      2. 6.4.2 Forced Continuous-Conduction Mode
      3. 6.4.3 Pre-Bias Start-up
  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  Choose the Switching Frequency and Operation Mode (MODE Pin)
        2. 7.2.2.2  Choose the Output Inductor (L)
        3. 7.2.2.3  Set the Current Limit (TRIP)
        4. 7.2.2.4  Choose the Output Capacitors (COUT)
        5. 7.2.2.5  Choose the Input Capacitors (CIN)
        6. 7.2.2.6  Feedback Network (FB Pin)
        7. 7.2.2.7  Soft Start Capacitor (SS/REFIN Pin)
        8. 7.2.2.8  EN Pin Resistor Divider
        9. 7.2.2.9  VCC Bypass Capacitor
        10. 7.2.2.10 BOOT Capacitor
        11. 7.2.2.11 Series BOOT Resistor and RC Snubber
        12. 7.2.2.12 PGOOD Pullup Resistor
      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 Documentation Support
      1. 8.1.1 Related Documentation
    2. 8.2 Support Resources
    3. 8.3 Receiving Notification of Documentation Updates
    4. 8.4 Trademarks
    5. 8.5 Glossary
    6. 8.6 Electrostatic Discharge Caution
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Ordering Information

6.3.7 Current Sense and Positive Overcurrent Protection

For a buck converter, during the on-time of the high-side FET, the switch current increases at a linear rate determined by input voltage, output voltage, and the output inductor value. During the on-time of the low-side FET, this current decreases at a linear rate determined by the output voltage and the output inductor value. The average value of the inductor current equals to the load current, IOUT.

The output overcurrent limit (OCL) in the TPS54J061 is implemented using a cycle-by-cycle valley current detect control circuit. The inductor current is monitored during the OFF state by measuring the low-side FET drain-to-source current. If the measured drain-to-source current of the low-side FET is above the current limit, the low-side FET stays ON until the current level becomes lower than the OCL level. This type of behavior reduces the average output current sourced by the device. During an overcurrent condition, the current to the load exceeds the current to the output capacitors and the output voltage tends to decrease. Eventually, when the output voltage falls below the undervoltage-protection threshold (80%), the UVP comparator shuts down the device after a wait time of 64 µs. The device will latch in the OFF state (both high-side and low-side FETs are latched off) and then restart after an approximate 14-ms delay. If the fault condition persists, the sensing detection, shut down and restart cycle repeats until the fault condition is removed.

If an OCL condition happens during start-up, then the device completes the charging of the soft-start capacitor, then trips UV when soft start is complete. Delay and attempted restart function follows as above.

The resistor, RTRIP connected from the TRIP pin to AGND sets the valley current limit threshold. Equation 4 calculates the RTRIP for a given current limit threshold.

Equation 4. TPS54J061

where

  • ILIM_VALLEY is the valley current limit threshold in A
  • RTRIP is TRIP resistor value in Ω

If an RTRIP value less than 3.74 kΩ is used, the TPS54J061 will default to an internally determined current limit clamp value.