SLUSAK2D August   2011  – April 2021 TPS53353

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 (1)
    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
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 5-V LDO and VREG Start-Up
      2. 7.3.2 Adaptive On-Time D-CAP™ Control and Frequency Selection
      3. 7.3.3 Ramp Signal
      4. 7.3.4 Adaptive Zero Crossing
      5. 7.3.5 Power-Good
      6. 7.3.6 Current Sense, Overcurrent and Short Circuit Protection
      7. 7.3.7 Overvoltage and Undervoltage Protection
      8. 7.3.8 UVLO Protection
      9. 7.3.9 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Small Signal Model
      2. 7.4.2 Enable, Soft Start, and Mode Selection
      3. 7.4.3 Auto-Skip Eco-mode™ Light Load Operation
      4. 7.4.4 Forced Continuous Conduction Mode
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Typical Application Circuit Diagram
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 External Component Selection
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Typical Application Circuit Diagram With Ceramic Output Capacitors
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
          1. 8.2.2.2.1 External Component Selection
          2. 8.2.2.2.2 External Component Selection Using All Ceramic Output Capacitors
        3. 8.2.2.3 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 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
    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

7.4.2 Enable, Soft Start, and Mode Selection

When the EN pin voltage rises above the enable threshold voltage (typically 1.2 V), the controller enters its start-up sequence. The internal LDO regulator starts immediately and regulates to 5 V at the VREG pin. The controller then uses the first 250 μs to calibrate the switching frequency setting resistance attached to the RF pin and stores the switching frequency code in internal registers. During this period, the MODE pin also senses the resistance attached to this pin and determines the soft-start time. Switching is inhibited during this phase. In the second phase, an internal DAC starts ramping up the reference voltage from 0 V to 0.6 V. Depending on the MODE pin setting, the ramping up time varies from 0.7 ms to 5.6 ms. Smooth and constant ramp-up of the output voltage is maintained during start-up regardless of load current.

Table 7-3 Soft-Start and MODE Settings
MODE SELECTIONACTIONSOFT-START TIME (ms)RMODE (kΩ)
Auto-skipPulldown to GND0.739
1.4100
2.8200
5.6475
Forced CCM(1)Connect to PGOOD0.739
1.4100
2.8200
5.6475
(1) Device enters FCCM after the PGOOD pin goes high when MODE is connected to PGOOD through the resistor RMODE.

After soft-start begins, the MODE pin becomes the input of an internal comparator which determines auto-skip or FCCM mode operation. If MODE voltage is higher than 1.3 V, the converter enters into FCCM mode. Otherwise it will be in auto-skip mode at light load condition. Typically, when FCCM mode is selected, the MODE pin is connected to PGOOD through the RMODE resistor, so that before PGOOD goes high the converter remains in auto-skip mode.