SLVSIO8 September   2026 TPS638221

PRODMIX  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison Table
  6. 5 Pin Configuration and Functions
  7. 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
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Control Scheme
        1. 7.3.1.1 Buck Operation
        2. 7.3.1.2 Boost Operation
        3. 7.3.1.3 Buck-Boost Operation
      2. 7.3.2 Operation Mode
        1. 7.3.2.1 PFM Operation
        2. 7.3.2.2 Forced-PWM Operation (FPWM)
        3. 7.3.2.3 Ultra-sonic Mode Operation
      3. 7.3.3 Undervoltage Lockout (UVLO)
      4. 7.3.4 Enable and Soft Start
      5. 7.3.5 Protection Functions
        1. 7.3.5.1 Input Voltage Protection (IVP)
        2. 7.3.5.2 Output Voltage Protection (OVP)
        3. 7.3.5.3 Current Limit Mode and Overcurrent Protection
        4. 7.3.5.4 Output Short Circuit Protection (Hiccup)
        5. 7.3.5.5 Thermal Shutdown
      6. 7.3.6 Power Good
      7. 7.3.7 Load Disconnect
      8. 7.3.8 Output Discharge
    4. 7.4 Device Functional Modes
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 3.3V Output Power Supply
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Inductor Selection
          2. 8.2.1.2.2 Output Capacitor Selection
          3. 8.2.1.2.3 Input Capacitor Selection
          4. 8.2.1.2.4 Setting the Output Voltage
        3. 8.2.1.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Third-Party Products Disclaimer
      2. 9.1.2 Third-Party Products Disclaimer
    2. 9.2 Documentation Support
      1. 9.2.1 Related Documentation
    3. 9.3 Receiving Notification of Documentation Updates
    4. 9.4 Support Resources
    5. 9.5 Trademarks
    6. 9.6 Electrostatic Discharge Caution
    7. 9.7 Export Control Notice
    8. 9.8 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information
    1.     67
8.2.1.2.4 Setting the Output Voltage

The output voltage is set by an external resistor divider. The resistor divider must be connected between VOUT, FB, and GND. The feedback voltage is 800mV nominal.

Keep the low-side resistor R2 (between FB and GND) below 200kΩ. The high-side resistor (between FB and VOUT) R1 is calculated with Equation 3.

Equation 3. TPS638221

where

  • VFB = 800mV

When FB is connected to AGND, the output voltage is fixed at 3.3V.

Table 8-4 Resistor Selection For Typical Output Voltages
VOUT R1 R2
3.3V 470kΩ 150kΩ
5V 680kΩ 130kΩ