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

7.3.2 Adaptive On-Time D-CAP™ Control and Frequency Selection

The TPS53353 does not have a dedicated oscillator to determine switching frequency. However, the device operates with pseudo-constant frequency by feed-forwarding the input and output voltages into the on-time one-shot timer. The adaptive on-time control adjusts the on-time to be inversely proportional to the input voltage and proportional to the output voltage (tON ∝ VOUT/VIN).

This makes the switching frequency fairly constant in steady state conditions over a wide input voltage range. The switching frequency is selectable from eight preset values by a resistor connected between the RF pin and GND or between the RF pin and the VREG pin as shown in Table 7-1. (Maintaining open resistance sets the switching frequency to 500 kHz.)

Table 7-1 Resistor and Switching Frequency
RESISTOR (RRF)
CONNECTIONS		SWITCHING FREQUENCY (fSW)
(kHz)
VALUE (kΩ)CONNECT TO
0GND250
187GND300
619GND400
OPENn/a500
866VREG650
309VREG750
124VREG850
0VREG970

The off-time is modulated by a PWM comparator. The VFB node voltage (the mid-point of resistor divider) is compared to the internal 0.6-V reference voltage added with a ramp signal. When both signals match, the PWM comparator asserts a set signal to terminate the off time (turn off the low-side MOSFET and turn on high-side MOSFET). The set signal is valid if the inductor current level is below the OCP threshold, otherwise the off time is extended until the current level falls below the threshold.

Figure 7-2 and Figure 7-3 show two on-time control schemes.

GUID-6C2661E4-C8D2-4859-8D80-97E83900CB5E-low.gifFigure 7-2 On-Time Control Without Ramp Compensation
GUID-F3FD68F8-9818-4712-B771-4D3AB74D8BAC-low.gifFigure 7-3 On-Time Control With Ramp Compensation