SBVS388B January   2021  – January 2022 TPS785-Q1

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 Diagrams
    3. 7.3 Feature Description
      1. 7.3.1 Foldback Current Limit
      2. 7.3.2 Output Enable
      3. 7.3.3 Active Discharge
      4. 7.3.4 Undervoltage Lockout (UVLO) Operation
      5. 7.3.5 Dropout Voltage
      6. 7.3.6 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Device Functional Mode Comparison
      2. 7.4.2 Normal Operation
      3. 7.4.3 Dropout Operation
      4. 7.4.4 Disabled
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Recommended Capacitor Types
      2. 8.1.2 Input and Output Capacitor Requirements
      3. 8.1.3 Adjustable Device Feedback Resistors
      4. 8.1.4 Load Transient Response
      5. 8.1.5 Exiting Dropout
      6. 8.1.6 Dropout Voltage
      7. 8.1.7 Reverse Current
      8. 8.1.8 Feed-Forward Capacitor (CFF)
      9. 8.1.9 Power Dissipation (PD)
        1. 8.1.9.1 Estimating Junction Temperature
        2. 8.1.9.2 Recommended Area for Continuous Operation
        3. 8.1.9.3 Power Dissipation versus Ambient Temperature
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
      3. 8.2.3 Application Curve
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Additional Layout Considerations
    2. 10.2 Layout Examples
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Device Nomenclature
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Support Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

8.1.3 Adjustable Device Feedback Resistors

The device requires external feedback divider resistors to set the output voltage. Figure 8-1 shows how the output voltage of an adjustable device can be configured from 1.2 V to 5.5 V by using a resistor divider network.

GUID-20201209-CA0I-XPMG-191F-JB22S61Z0NKK-low.gif Figure 8-1 Adjustable Operation

Equation 2 calculates the values of the R1 and R2 resistors to set the output voltage:

Equation 2. VOUT = VFB × (1 + R1 / R2) + IFB × R1

To disregard the effect of the FB pin current error term in Equation 2 and to achieve best accuracy, choose R2 to be equal to or smaller than 550 kΩ so that the current flowing through R1 and R2 is at least 100 times larger than the IFB current listed in the Electrical Characteristics table. Lowering the value of R2 increases the immunity against noise injection. Increasing the value of R2 reduces the quiescent current for achieving higher efficiency at low load currents. Equation 3 calculates the setting that provides the maximum feedback divider series resistance.

Equation 3. (R1 + R2) ≤ VOUT / (IFB × 100)