SLVSE72B September   2017  – June 2018 TPS565208

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
      2.      TPS565208 Load Regulation
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin 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 Adaptive On-Time Control and PWM Operation
      2. 7.3.2 Soft Start and Pre-Biased Soft Start
      3. 7.3.3 Current Protection
      4. 7.3.4 Undervoltage Lockout (UVLO) Protection
      5. 7.3.5 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Normal Operation
      2. 7.4.2 Standby Operation
  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
        5. 8.2.2.5 Bootstrap 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 Development Support
      1. 11.1.1 Custom Design With WEBENCH® Tools
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information
    1. 12.1 Package Option Addendum
      1. 12.1.1 Packaging Information
      2. 12.1.2 Tape and Reel 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 double pole at:

Equation 2. TPS565208 Eq_03_SLVSD90.gif

At low frequencies, 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 rapidly. D-CAP2 introduces a high frequency zero that reduces the gain roll off to –20 dB per decade and increases the phase to 90° one decade above the zero frequency. The inductor and capacitor for the output filter must be selected so that the double pole of Equation 2 is located below the high frequency zero but close enough that the phase boost provided be the high frequency zero provides adequate phase margin for a stable circuit. To meet this requirement use the values recommended in Table 2.

Table 2. Recommended Component Values

OUTPUT VOLTAGE (V) R1 (kΩ) R2 (kΩ) L1 (µH) C8 + C9 (µF)
MIN TYP MAX
1 3.09 10.0 1 2.2 4.7 20 to 68
1.05 3.74 10.0 1 2.2 4.7 20 to 68
1.2 5.76 10.0 1 2.2 4.7 20 to 68
1.5 9.53 10.0 1.5 2.2 4.7 20 to 68
1.8 13.7 10.0 1.5 2.2 4.7 20 to 68
2.5 22.6 10.0 2.2 2.2 4.7 20 to 68
3.3 33.2 10.0 2.2 2.2 4.7 20 to 68
5 54.9 10.0 3.3 3.3 4.7 20 to 68
6.5 75 10.0 3.3 3.3 4.7 20 to 68

The inductor peak-to-peak ripple current, peak current and RMS current are calculated using Equation 3, Equation 4, and Equation 5. 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.

Use 550 kHz for ƒSW. Make sure the chosen inductor is rated for the peak current of Equation 4 and the RMS current of Equation 6.

Equation 3.
Equation 4. TPS565208 Eq_Ipeak2_SLVSE72.gif
Equation 5. TPS565208 Eq_ILorms2_SLVSE72.gif

For this design example, the calculated peak current is 5.4 A and the calculated RMS current is 5 A. The inductor used is a WE 744311220 with a peak current rating of 13 A and an RMS current rating of 9 A.

The capacitor value and ESR determines the amount of output voltage ripple. The TPS565208 is intended for use with ceramic or other low ESR capacitors. Recommended values range from 20 µF to 68 µF. Use Equation 6 to determine the required RMS current rating for the output capacitor.

Equation 6. TPS565208 Eq_07_SLVSD90.gif

For this design two TDK C3216X5R0J226M 22-µF output capacitors are used. The typical ESR is 2 mΩ each. The calculated RMS current is 0.229 A.