SLUSEN2 April   2022 TPS564242 , TPS564247

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
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 PWM Operation and D-CAP3 Control
      2. 7.3.2 Eco-Mode Control
      3. 7.3.3 Soft Start and Prebiased Soft Start
      4. 7.3.4 Overvoltage Protection
      5. 7.3.5 Large Duty Operation
      6. 7.3.6 Current Protection and Undervoltage Protection
      7. 7.3.7 Undervoltage Lockout (UVLO) Protection
      8. 7.3.8 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Eco-Mode Operation
      2. 7.4.2 FCCM Mode Control
  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 Custom Design With WEBENCH® Tools
        2. 8.2.2.2 Output Voltage Resistors Selection
        3. 8.2.2.3 Output Filter Selection
        4. 8.2.2.4 Input Capacitor Selection
      3. 8.2.3 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. 11.1.2 Development Support
        1. 11.1.2.1 Custom Design With WEBENCH® Tools
    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
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

8.2.2.3 Output Filter Selection

The LC filter used as the output filter has a double pole at Equation 4. In this equation, COUT should use its effective value after derating, not its nominal value.

Equation 4. GUID-75C9B671-2032-4F17-92A3-6C909D7396B5-low.gif

For any control topology that is compensated internally, there is a range of the output filter it can support. At low frequency, the overall loop gain is set by the output set-point resistor divider network and the internal gain of the device. The low frequency phase is 180°. At the output filter pole frequency, the gain rolls off at a –40 dB per decade rate and the phase drops has a 180 degree drop. The internal ripple generation network introduces a high-frequency zero that reduces the gain roll off from –40 dB to –20 dB per decade and leads the 90 degree phase boost. The internal ripple injection high-frequency zero is about 100 kHz. The inductor and capacitor selected for the output filter is recommended that the double pole is located about 30 kHz, so that the phase boost provided by this high-frequency zero provides adequate phase margin for the stability requirement. The crossover frequency of the overall system should usually be targeted to be less than one-third of the switching frequency (FSW).

Table 8-2 Recommended Component Values
Output Voltage (V) R1 (kΩ) R2 (kΩ) Minimum L1 (μH) Typical L1 (μH)(1) Maximum L1 (μH) Minimum COUT (μF) Typical COUT (μF)(1) Maximum COUT (μF) CFF (pF)
0.6 0 10.0 0.33 0.82 2.2 22 44 100 —
1.05 7.5 10.0 0.47 0.82 2.2 22 44 100 —
1.8 20.0 10.0 0.68 1.0 2.2 22 44 100 10–470
2.5 95.0 30.0 1 1.5 4.7 22 44 100 10–470
3.3 135.0 30.0 1.2 1.5 4.7 22 44 100 10–470
5 220.0 30.0 1.5 1.8 4.7 22 44 100 10–470
7 320.0 30.0 1.8 2.2 4.7 22 44 100 10–470

The inductor peak-to-peak ripple current, peak current, and RMS current are calculated using Equation 5, Equation 6, and Equation 7. The inductor saturation current rating must be greater than the calculated peak current and the RMS or heating current rating must be greater than the calculated RMS current.

Equation 5. GUID-C3150711-BA14-43CA-AFBE-BEBFAB8C2341-low.gif
Equation 6. GUID-64C06B84-40ED-4173-87FC-36A496B452E8-low.gif
Equation 7. GUID-F9038776-F0F7-46C9-B5D5-5BB2E9960385-low.gif

For this design example, the calculated peak current is 4.8 A and the calculated RMS current is 4.2 A. The inductor used is WE744311100 with 8-A saturation current and 15-A rated current.

The capacitor value and ESR determines the amount of output voltage ripple. The TPS56424x are intended for use with ceramic or other low-ESR capacitors. Use Equation 8 to determine the required RMS current rating for the output capacitor.

Equation 8. GUID-2E464547-0BD4-48F3-87EA-FACC0B8CF028-low.gif

For this design, four MuRata GRM21BR61A226ME44L 22-µF output capacitors are used. The typical ESR is 2 mΩ each. The calculated RMS current is 0.47 A and each output capacitor is rated for 4 A.