SNVSC10 March   2022 LM25143

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Description (continued)
  6. 6 Device Comparison Table
  7. 7 Pin Configuration and Functions
  8. 8 Specifications
    1. 8.1 Absolute Maximum Ratings
    2. 8.2 ESD Ratings
    3. 8.3 Recommended Operating Conditions
    4. 8.4 Thermal Information
    5. 8.5 Electrical Characteristics
    6. 8.6 Switching Characteristics
    7. 8.7 Typical Characteristics
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1  Input Voltage Range (VIN)
      2. 9.3.2  High-Voltage Bias Supply Regulator (VCC, VCCX, VDDA)
      3. 9.3.3  Enable (EN1, EN2)
      4. 9.3.4  Power-Good Monitor (PG1, PG2)
      5. 9.3.5  Switching Frequency (RT)
      6. 9.3.6  Clock Synchronization (DEMB)
      7. 9.3.7  Synchronization Out (SYNCOUT)
      8. 9.3.8  Spread Spectrum Frequency Modulation (DITH)
      9. 9.3.9  Configurable Soft Start (SS1, SS2)
      10. 9.3.10 Output Voltage Setpoint (FB1, FB2)
      11. 9.3.11 Minimum Controllable On Time
      12. 9.3.12 Error Amplifier and PWM Comparator (FB1, FB2, COMP1, COMP2)
      13. 9.3.13 Slope Compensation
      14. 9.3.14 Inductor Current Sense (CS1, VOUT1, CS2, VOUT2)
        1. 9.3.14.1 Shunt Current Sensing
        2. 9.3.14.2 Inductor DCR Current Sensing
      15. 9.3.15 Hiccup Mode Current Limiting (RES)
      16. 9.3.16 High-Side and Low-Side Gate Drivers (HO1/2, LO1/2, HOL1/2, LOL1/2)
      17. 9.3.17 Output Configurations (MODE, FB2)
        1. 9.3.17.1 Independent Dual-Output Operation
        2. 9.3.17.2 Single-Output Interleaved Operation
        3. 9.3.17.3 Single-Output Multiphase Operation
    4. 9.4 Device Functional Modes
      1. 9.4.1 Standby Modes
      2. 9.4.2 Diode Emulation Mode
      3. 9.4.3 Thermal Shutdown
  10. 10Application and Implementation
    1. 10.1 Application Information
      1. 10.1.1 Power Train Components
        1. 10.1.1.1 Buck Inductor
        2. 10.1.1.2 Output Capacitors
        3. 10.1.1.3 Input Capacitors
        4. 10.1.1.4 Power MOSFETs
        5. 10.1.1.5 EMI Filter
      2. 10.1.2 Error Amplifier and Compensation
    2. 10.2 Typical Applications
      1. 10.2.1 Design 1 – 5-V and 3.3-V Dual-Output Buck Regulator for Computing Applications
        1. 10.2.1.1 Design Requirements
        2. 10.2.1.2 Detailed Design Procedure
          1. 10.2.1.2.1 Custom Design With WEBENCH® Tools
          2. 10.2.1.2.2 Custom Design With Excel Quickstart Tool
          3. 10.2.1.2.3 Inductor Calculation
          4. 10.2.1.2.4 Current-Sense Resistance
          5. 10.2.1.2.5 Output Capacitors
          6. 10.2.1.2.6 Input Capacitors
          7. 10.2.1.2.7 Compensation Components
        3. 10.2.1.3 Application Curves
      2. 10.2.2 Design 2 – Two-Phase, 15-A, 2.1-MHz Single-Output Buck Regulator for Server Applications
        1. 10.2.2.1 Design Requirements
        2. 10.2.2.2 Detailed Design Procedure
        3. 10.2.2.3 Application Curves
      3. 10.2.3 Design 3 – Two-Phase, 50-A, 300-kHz Single-Output Buck Regulator for ASIC Power Applications
        1. 10.2.3.1 Design Requirements
        2. 10.2.3.2 Detailed Design Procedure
        3. 10.2.3.3 Application Curves
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
      1. 12.1.1 Power Stage Layout
      2. 12.1.2 Gate-Drive Layout
      3. 12.1.3 PWM Controller Layout
      4. 12.1.4 Thermal Design and Layout
      5. 12.1.5 Ground Plane Design
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Device Support
      1. 13.1.1 Third-Party Products Disclaimer
      2. 13.1.2 Development Support
        1. 13.1.2.1 Custom Design With WEBENCH® Tools
    2. 13.2 Documentation Support
      1. 13.2.1 Related Documentation
        1. 13.2.1.1 PCB Layout Resources
        2. 13.2.1.2 Thermal Design Resources
    3. 13.3 Receiving Notification of Documentation Updates
    4. 13.4 Support Resources
    5. 13.5 Trademarks
    6. 13.6 Electrostatic Discharge Caution
    7. 13.7 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

10.1.1.3 Input Capacitors

Input capacitors are necessary to limit the input ripple voltage to the buck power stage due to switching-frequency AC currents. TI recommends using X7S or X7R dielectric ceramic capacitors to provide low impedance and high RMS current rating over a wide temperature range. To minimize the parasitic inductance in the switching loop, position the input capacitors as close as possible to the drain of the high-side MOSFET and the source of the low-side MOSFET. Use Equation 19 to calculate the input capacitor RMS current for a single-channel buck regulator.

Equation 19. GUID-61BCEB66-A882-40B7-9A98-A392683BDB55-low.gif

The highest input capacitor RMS current occurs at D = 0.5, at which point the RMS current rating of the input capacitors is greater than half the output current.

Ideally, the DC component of input current is provided by the input voltage source and the AC component by the input filter capacitors. Neglecting inductor ripple current, the input capacitors source current of amplitude (IOUT − IIN) during the D interval and sink IIN during the 1−D interval. Thus, the input capacitors conduct a square-wave current of peak-to-peak amplitude equal to the output current. It follows that the resultant capacitive component of AC ripple voltage is a triangular waveform. Together with the ESR-related ripple component, use Equation 20 to calculate the peak-to-peak ripple voltage amplitude.

Equation 20. GUID-82082AEC-FC37-4024-BC69-18B9142E1C69-low.gif

Use Equation 21 to calculate the input capacitance required for a particular load current, based on an input voltage ripple specification of ΔVIN.

Equation 21. GUID-DD1C55AB-D737-4756-9A7D-C9FC2F9E8B07-low.gif

Low-ESR ceramic capacitors can be placed in parallel with higher valued bulk capacitance to provide optimized input filtering for the regulator and damping to mitigate the effects of input parasitic inductance resonating with high-Q ceramics. One bulk capacitor of sufficiently high current rating and four 10-μF 50-V X7R ceramic decoupling capacitors are usually sufficient for 12-V battery automotive applications. Select the input bulk capacitor based on its ripple current rating and operating temperature range.

Of course, a two-channel buck regulator with 180° out-of-phase interleaved switching provides input ripple current cancellation and reduced input capacitor current stress. The previous equations represent valid calculations when one output is disabled and the other output is fully loaded.