SLVS325D March   2001  – February 2018 TPS791

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic: Fixed Output
      2.      Simplified Schematic: Adjustable Output
  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 Diagrams
    3. 7.3 Feature Description
      1. 7.3.1 Power Dissipation and Junction Temperature
      2. 7.3.2 Programming the TPS79101 Adjustable Regulator
      3. 7.3.3 Regulator Protection
    4. 7.4 Device Functional Modes
      1. 7.4.1 Normal Operation
      2. 7.4.2 Dropout Operation
      3. 7.4.3 Disabled
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 External Capacitor Requirements
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
      3. 8.2.3 Application Curves
    3. 8.3 Do's and Don'ts
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Board Layout Recommendation to Improve PSRR and Noise Performance
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Receiving Notification of Documentation Updates
    2. 11.2 Community Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

7.3.2 Programming the TPS79101 Adjustable Regulator

The output voltage of the TPS79101 adjustable regulator is programmed using an external resistor divider; see Figure 32. The output voltage is calculated using:

Equation 3. TPS791 Q_vo_ref_r1-lvs325.gif

where

  • VREF = 1.2246 V typ (the internal reference voltage)

Select resistors R1 and R2 for approximately a 50-µA divider current. Lower value resistors can be used for improved noise performance, but the solution consumes more power. Avoid higher resistor values because leakage current into or out of FB across R1, R2 creates an offset voltage that artificially increases or decreases the feedback voltage and thus erroneously decreases or increases VOUT. The recommended design procedure is to choose R2 = 30.1 kΩ to set the divider current at 50 µA, C1 = 15 pF for stability, and then calculate R1 using:

Equation 4. TPS791 Q_r1_vo_r2-lvs325.gif

In order to improve the stability of the adjustable version, a small compensation capacitor is suggested to be placed between OUT and FB. For voltages < 1.8 V, the value of this capacitor must be 100 pF. For voltages > 1.8 V, the approximate value of this capacitor can be calculated as:

Equation 5. TPS791 Q_c1_r1_r2-lvs325.gif

The table in Figure 34 shows the suggested value of this capacitor for several resistor ratios. If this capacitor is not used (such as in a unity-gain configuration) or if an output voltage < 1.8 V is chosen, then the minimum recommended output capacitor is 2.2 µF instead of 1 µF.

TPS791 ai_adj_ldo-lvs325.gifFigure 34. TPS79101 Adjustable LDO Regulator Programming