SNVSBT8 March   2021 TPSM13604H

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 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
      1. 7.1.1 COT Control Circuit Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Output Overvoltage Comparator
      2. 7.3.2 Current Limit
      3. 7.3.3 Thermal Protection
      4. 7.3.4 Zero Coil Current Detection
      5. 7.3.5 Prebiased Start-up
    4. 7.4 Device Functional Modes
      1. 7.4.1 Discontinuous Conduction and Continuous Conduction Modes
  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 Design Steps for the TPSM13604 Application
          1. 8.2.2.1.1 Enable Divider, RENT, and RENB Selection
          2. 8.2.2.1.2 Output Voltage Selection
          3. 8.2.2.1.3 Soft-Start Capacitor, CSS, Selection
          4. 8.2.2.1.4 Output Capacitor, CO, Selection
            1. 8.2.2.1.4.1 Capacitance
            2. 8.2.2.1.4.2 ESR
          5. 8.2.2.1.5 Input Capacitor, CIN, Selection
          6. 8.2.2.1.6 ON-Time, RON, Resistor Selection
            1. 8.2.2.1.6.1 Discontinuous Conduction and Continuous Conduction Mode Selection
      3. 8.2.3 Application Curve
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Power Module SMT Guidelines
    2. 10.2 Layout Example
      1. 10.2.1 Power Dissipation and Board Thermal Requirements
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Support Resources
    5. 11.5 Trademarks
    6. 11.6 Glossary
    7. 11.7 Electrostatic Discharge Caution
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information
8.2.2.1.6 ON-Time, RON, Resistor Selection

Many designs begin with a desired switching frequency in mind. For 4-A applications, 300 kHz is recommended. Equation 16 can be used to calculate the RON value.

Equation 16. fSW(CCM) ≊ VO / (1.3 × 10-10 × RON)

This can be rearranged as:

Equation 17. RON ≊ VO / (1.3 × 10-10 × fSW(CCM)

The selection of RON and fSW(CCM) must be confined by limitations in the on-time and off-time for Section 7.1.1.

The on-time of the TPSM13604 timer is determined by the resistor RON and the input voltage VIN. It is calculated as follows:

Equation 18. tON = (1.3 × 10-10 x RON) / VIN

The inverse relationship of tON and VIN gives a nearly constant switching frequency as VIN is varied. RON must be selected such that the on-time at maximum VIN is greater than 150 ns. The on-timer has a limiter to ensure a minimum of 150 ns for tON. This limits the maximum operating frequency, which is governed by Equation 19.

Equation 19. fSW(MAX) = VO / (VIN(MAX) × 150 ns)

This equation can be used to select RON if a certain operating frequency is desired so long as the minimum on-time of 150 ns is observed. The limit for RON can be calculated as follows:

Equation 20. RON ≥ VIN(MAX) × 150 nsec / (1.3 × 10-10)

If RON calculated in Equation 17 is less than the minimum value determined in Equation 20, a lower frequency should be selected. Alternatively, VIN(MAX) can also be limited to keep the frequency unchanged.

Additionally, the minimum off-time of 260 ns (typical) limits the maximum duty ratio. Larger RON (lower FSW) must be selected in any application requiring large duty ratio.