SBVS068I February   2006  – January 2016 TPS717


  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  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. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagrams
    3. 7.3 Feature Description
      1. 7.3.1 Internal Current Limit
      2. 7.3.2 Shutdown
      3. 7.3.3 Startup and Noise Reduction Capacitor
      4. 7.3.4 Undervoltage Lockout (UVLO)
      5. 7.3.5 Minimum Load
      6. 7.3.6 Thermal 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. Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Transient Response
      2. 8.1.2 Input and Output Capacitor Requirements
      3. 8.1.3 Dropout Voltage
      4. 8.1.4 Output Noise
    2. 8.2 Typical Applications
      1. 8.2.1 Application for Fixed Voltage Versions and Adjustable Voltage Version
        1. Design Requirements
        2. Detailed Design Procedure
        3. Application Curve
      2. 8.2.2 Powering a PLL Integrated on an SOC
    3. 8.3 Do's and Don'ts
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Board Layout Recommendations to Improve PSRR and Noise Performance
    2. 10.2 Layout Examples
    3. 10.3 Power Dissipation
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Development Support
        1. Evaluation Module
      2. 11.1.2 Device Nomenclature
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    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



10 Layout

10.1 Layout Guidelines

For best overall performance, place all circuit components on the same side of the circuit board and as near as practical to the respective LDO pin connections. Place ground return connections to the input and output capacitor, and to the LDO ground pin as close to the GND pin as possible, connected by wide, component-side, copper surface area. The use of vias and long traces to create LDO component connections is strongly discouraged and negatively affects system performance. This grounding and layout scheme minimizes inductive parasitics, and thereby reduces load-current transients, minimizes noise, and increases circuit stability. A ground reference plane is also recommended and is either embedded in the printed circuit board (PCB) itself or located on the bottom side of the PCB opposite the components. This reference plane serves to assure accuracy of the output voltage, shields the LDO from noise, and functions similar to a thermal plane to spread (or sink) heat from the LDO device when connected to the thermal pad. In most applications, this ground plane is necessary to meet thermal requirements.

10.1.1 Board Layout Recommendations to Improve PSRR and Noise Performance

To improve ac performance (such as PSRR, output noise, and transient response), TI recommends that the board be designed with separate ground planes for VIN and VOUT, with each ground plane connected only at the GND pin of the device. In addition, the ground connection for the bypass capacitor must connect directly to the GND pin of the device.

10.2 Layout Examples

TPS717 DRV_Layout_fixed_lvsbm4.gif
1. Circles within thermal pad area indicate vias to other layers on the board, for electrical connections or thermal conduction.
Figure 37. Fixed Voltage Layout
TPS717 DRV_Layout_adjust_lvsbm4.gif
1. Circles within thermal pad area indicate vias to other layers on the board, for electrical connections or thermal conduction.
Figure 38. Adjustable Voltage Layout

10.3 Power Dissipation

The ability to remove heat from the die is different for each package type, presenting different considerations in the printed circuit board (PCB) layout. The PCB area around the device that is free of other components moves the heat from the device to the ambient air. Performance data for JEDEC low- and high-K boards are given in the Thermal Information table. Using heavier copper increases the effectiveness in removing heat from the device. The addition of plated through-holes to heat-dissipating layers also improves the heatsink effectiveness.

Power dissipation depends on input voltage and load conditions. Power dissipation (PD) is equal to the product of the output current times the voltage drop across the output pass element (VIN to VOUT), and is approximated in Equation 4:

Equation 4. TPS717 q_pd_bvs067.gif

A better method of estimating the thermal measure comes from using the thermal metrics ΨJT and ΨJB; see the Thermal Information table. These metrics are a more accurate representation of the heat transfer characteristics of the die and the package than RθJA. The junction temperature can be estimated with Equation 5.

Equation 5. TPS717 q_new_metrics_bvs066.gif


  • PD is the power dissipation given by Equation 4,
  • TT is the temperature at the center-top of the device package,
  • TB is the PCB temperature measured 1 mm away from the device package on the PCB surface.


Both TT and TB can be measured on actual application boards using a thermo‐gun (an infrared thermometer).

For more information about measuring TT and TB, see the application note Using New Thermal Metrics (SBVA025), available for download at