SLVSAA4G June   2010  – February 2018 TPS65251

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Typical Application Schematic
  4. 4 Revision History
  5. 5 Description (continued)
  6. 6 Pin Configuration and Functions
    1.     Pin Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Adjustable Switching Frequency
      2. 8.3.2  Synchronization
      3. 8.3.3  Out-of-Phase Operation
      4. 8.3.4  Delayed Start-Up
      5. 8.3.5  Soft-Start Time
      6. 8.3.6  Adjusting the Output Voltage
      7. 8.3.7  Input Capacitor
      8. 8.3.8  Bootstrap Capacitor
      9. 8.3.9  Error Amplifier
      10. 8.3.10 Loop Compensation
      11. 8.3.11 Slope Compensation
      12. 8.3.12 Powergood
      13. 8.3.13 Current Limit Protection
      14. 8.3.14 Overvoltage Transient Protection
      15. 8.3.15 Thermal Shutdown
    4. 8.4 Device Functional Modes
      1. 8.4.1 Low-Power Mode Operation
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1  Loop Compensation Circuit
        2. 9.2.2.2  Selecting the Switching Frequency
        3. 9.2.2.3  Output Inductor Selection
        4. 9.2.2.4  Output Capacitor
        5. 9.2.2.5  Input Capacitor
        6. 9.2.2.6  Soft-Start Capacitor
        7. 9.2.2.7  Bootstrap Capacitor Selection
        8. 9.2.2.8  Adjustable Current Limiting Resistor Selection
        9. 9.2.2.9  Output Voltage and Feedback Resistors Selection
        10. 9.2.2.10 Compensation
        11. 9.2.2.11 3.3-V and 6.5-V LDO Regulators
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
    3. 11.3 Power Dissipation
  12. 12Device and Documentation Support
    1. 12.1 Receiving Notification of Documentation Updates
    2. 12.2 Community Resources
    3. 12.3 Trademarks
    4. 12.4 Electrostatic Discharge Caution
    5. 12.5 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

8.1 Overview

TPS65251 is a power management IC with three step-down buck converters. Both high-side and low-side MOSFETs are integrated to provide fully synchronous conversion with higher efficiency. TPS65251 can support 4.5-V to 18-V input supply, high load current, 300-kHz to 2.2-MHz clocking. The buck converters have an optional PSM mode, which can improve power dissipation during light loads. Alternatively, the device implements a constant frequency mode by connecting the LOW_P pin to ground. The wide switching frequency of 300 kHz to 2.2 MHz allows for efficiency and size optimization. The switching frequency is adjustable by selecting a resistor to ground on the ROSC pin. The SYNC pin also provides a means to synchronize the power converter to an external signal. Input ripple is reduced by 180 degree out-of-phase operation between Buck 1 and Buck 2. Buck 3 operates in phase with Buck 2.

All three buck converters have peak current mode control which simplifies external frequency compensation. A traditional type II compensation network can stabilize the system and achieve fast transient response. Moreover, an optional capacitor in parallel with the upper resistor of the feedback divider provides one more zero and makes the crossover frequency over 100 kHz.

Each buck converter has an individual current limit, which can be set up by a resistor to ground from the RLIM pin. The adjustable current limiting enables high efficiency design with smaller and less expensive inductors.

The device has two built-in LDO regulators. During a standby mode, the 3.3-V LDO and the 6.5-V LDO can be used to drive MCU and other active loads. By this, the system is able to turn off the three buck converters and improve the standby efficiency.

The device has a powergood comparator monitoring the output voltage. Each converter has its own soft-start and enable pins, which provide independent control and programmable soft-start.