SLVSAI4E September   2010  – September 2024 TPS74801-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 = 50 mA
    7. 5.7 Typical Characteristics: IOUT = 1 A
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagrams
    3. 6.3 Feature Description
      1. 6.3.1 Programmable Soft-Start
      2. 6.3.2 Sequencing Requirements
      3. 6.3.3 Output Noise
      4. 6.3.4 Enable and Shutdown
      5. 6.3.5 Power Good
      6. 6.3.6 Internal Current Limit
      7. 6.3.7 Thermal Protection
    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
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1 Input, Output, and Bias Capacitor Requirements
        2. 7.2.2.2 Transient Response
      3. 7.2.3 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
        1. 7.4.1.1 Layout Recommendations and Power Dissipation
        2. 7.4.1.2 Estimating Junction Temperature
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Documentation Support
      1. 8.1.1 Related Documentation
      2. 8.1.2 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

Package Options

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

6.3.1 Programmable Soft-Start

The TPS74801-Q1 features a programmable, monotonic, voltage-controlled soft-start that is set with an external capacitor (CSS). This feature is important for many applications because soft-start eliminates power-up initialization problems when powering FPGAs, DSPs, or other processors. The controlled voltage ramp of the output also reduces peak inrush current during start-up, minimizing start-up transient events to the input power bus.

To achieve a linear and monotonic soft-start, the TPS74801-Q1 error amplifier tracks the voltage ramp of the external soft-start capacitor until the voltage exceeds the internal reference. The soft-start ramp time depends on the soft-start charging current (ISS), soft-start capacitance (CSS), and the internal reference voltage (VREF), and can be calculated using Equation 1:

Equation 1. TPS74801-Q1

If large output capacitors are used, the device current limit (ICL) and the output capacitor can set the start-up time. In this case, the start-up time is given by Equation 2:

Equation 2. TPS74801-Q1

where:

  • VOUT(NOM) is the nominal output voltage
  • COUT is the output capacitance
  • ICL(MIN) is the minimum current limit for the device

In applications where monotonic start-up is required, the soft-start time given by Equation 1 must be set greater than Equation 2.

The maximum recommended soft-start capacitor is 0.015 μF. Larger soft-start capacitors can be used and do not damage the device; however, the soft-start capacitor discharge circuit can possibly be unable to fully discharge the soft-start capacitor when enabled. Soft-start capacitors larger than 0.015 μF can be a problem in applications where the enable pin must be rapidly pulsed while still requiring the device to soft-start from ground. CSS must be low-leakage; X7R, X5R, or C0G dielectric materials are preferred. See Table 7-3 for suggested soft-start capacitor values.