SBVS425B December   2022  – June 2025 TPS748A-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Typical Characteristics: IOUT = 50mA
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Enable and Shutdown
      2. 6.3.2 Active Discharge
      3. 6.3.3 Power-Good Output (PG)
      4. 6.3.4 Internal Current Limit
      5. 6.3.5 Thermal Shutdown Protection (TSD)
    4. 6.4 Device Functional Modes
      1. 6.4.1 Normal Operation
      2. 6.4.2 Dropout Operation
      3. 6.4.3 Disabled
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 Input, Output, and Bias Capacitor Requirements
      2. 7.1.2 Dropout Voltage
      3. 7.1.3 Output Noise
      4. 7.1.4 Estimating Junction Temperature
      5. 7.1.5 Soft Start, Sequencing, and Inrush Current
      6. 7.1.6 Power-Good Operation
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
      3. 7.2.3 Application Curve
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Device Nomenclature
    2. 8.2 Receiving Notification of Documentation Updates
    3. 8.3 Support Resources
    4. 8.4 Trademarks
    5. 8.5 Electrostatic Discharge Caution
    6. 8.6 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

7.4.1 Layout Guidelines

An optimized layout greatly improves transient performance, PSRR, and noise. To minimize voltage drop on the device input during load transients, connect the capacitance on IN and BIAS as close as possible to the device. This capacitance also minimizes the effects of parasitic inductance and resistance of the input source and, therefore, improves stability. To achieve excellent transient performance and accuracy, connect the top side of R1 in Figure 7-2 as close as possible to the load. If BIAS is connected to IN, connect BIAS as close to the sense point of the input supply as possible. This connection minimizes the voltage drop on BIAS during transient conditions and improves turn-on response.

Knowing the device power dissipation and proper sizing of the thermal plane connected to the thermal pad is critical to avoiding thermal shutdown and providing reliable operation. Power dissipation of the device is calculated using Equation 11 and depends on input voltage and load conditions.

Equation 11. TPS748A-Q1

Power dissipation is minimized and greater efficiency achieved by using the lowest possible input voltage necessary to achieve the required output voltage regulation.

On the VSON (DRC) package, the primary conduction path for heat is through the exposed pad to the printed circuit board (PCB). The pad is connected to ground or left floating. However, attach the thermal pad to an appropriate amount of copper PCB area to make sure the device does not overheat. The maximum junction-to-ambient thermal resistance is calculated using Equation 12 and depends on the maximum ambient temperature, maximum device junction temperature, and power dissipation of the device.

Equation 12. TPS748A-Q1

The minimum amount of PCB copper area needed for appropriate heat sinking (estimated by Figure 7-4) is determined by knowing the maximum RθJA.

TPS748A-Q1 RθJA vs Board Size
The RθJA value at board size of 9 in2 (that is, 3in × 3in) is a JEDEC standard.
Figure 7-4 RθJA vs Board Size

Figure 7-4 shows the variation of RθJA as a function of ground plane copper area in the board. This figure is intended only as a guideline to demonstrate the effects of heat spreading in the ground plane. This figure is not intended to be used to estimate actual thermal performance in real application environments.

Note: When the device is mounted on an application PCB, use ΨJT and ΨJB, as explained in the Estimating Junction Temperature section.