SLUSDR7B January   2020  – April 2021 TPS562207

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 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 Output Voltage Resistors Selection
        2. 8.2.2.2 Output Filter Selection
        3. 8.2.2.3 Input Capacitor Selection
        4. 8.2.2.4 Bootstrap Capacitor Selection
      3. 8.2.3 Application Curves
  9. 9 Layout
    1. 9.1 Layout Guidelines
    2. 9.2 Layout Example
  10. 10Device and Documentation Support
    1. 10.1 Receiving Notification of Documentation Updates
    2. 10.2 Support Resources
    3. 10.3 Trademarks
    4. 10.4 Electrostatic Discharge Caution
    5. 10.5 Glossary
  11. 11Mechanical, Packaging, and Orderable Information

Package Options

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

8.2.2.2 Output Filter Selection

The LC filter used as the output filter has double pole at:

Equation 2. GUID-7E8F0DA6-7E08-404F-8D1F-D47EE4268EA1-low.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 8-2.

Table 8-2 Recommended Component Values
OUTPUT VOLTAGE (V)R1 (kΩ)R2 (kΩ)TYP L1 (µH)C8 + C9 (µF)CFF (pF)
MinTypMax
0.850.5510.02.22044110-
0.91.210.02.22044110-
12.410.02.22044110-
1.05310.02.22044110-
1.24.910.02.22044110-
1.58.610.02.22044110-
1.812.310.02.22044110-
2.52110.03.32044110-
3.33110.03.3204411010-220
55210.04.7204411010-220
6.570.510.04.7204411010-220

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.

Equation 3. GUID-FCFD3B60-523A-47BD-A681-DCBEC0973929-low.gif
Equation 4. GUID-7EC792B3-F9D7-48B0-8873-1AE2AACBE3EB-low.gif
Equation 5. GUID-E60CA3DE-9ADB-434B-A878-CB7118F1E716-low.gif

For this design example, the calculated peak current is 2.35 A and the calculated RMS current is 2.01 A. The inductor used is a WE 74437349022 with an RMS current rating of 7.5 A.

The capacitor value and ESR determines the amount of output voltage ripple. TPS562207 is intended for use with ceramic or other low ESR capacitors. Recommended values range from 20 µF to 110 µF. Use Equation 6 to determine the required RMS current rating for the output capacitor.

Equation 6. GUID-EE933A26-632C-4DC4-A21B-2CBD9C2276A2-low.gif

For this design two MuRata GRM21BR61A226ME44L 22-µF output capacitors are used. The typical ESR is 2 mΩ each. The calculated RMS current is 0.286 A and each output capacitor is rated for 4 A.