SLVSGC1B December   2021  – August 2024 TPS63901

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
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Trapezoidal Current Control
      2. 6.3.2 Device Enable and Disable
      3. 6.3.3 Soft Start
      4. 6.3.4 Input Current Limit
      5. 6.3.5 Dynamic Voltage Scaling
      6. 6.3.6 Device Configuration (Resistor-to-Digital Interface)
      7. 6.3.7 SEL Pin
      8. 6.3.8 Short-Circuit Protection
        1. 6.3.8.1 Current Limit Setting = 'Unlimited'
        2. 6.3.8.2 Current Limit Setting = 1 mA to 100 mA
      9. 6.3.9 Thermal Shutdown
    4. 6.4 Device Functional Modes
  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 Inductor Selection
        2. 7.2.2.2 Output Capacitor Selection
        3. 7.2.2.3 Input Capacitor Selection
        4. 7.2.2.4 Setting The Output Voltage
      3. 7.2.3 Application Curves
  9. 8 Power Supply Recommendations
  10. 9 Layout
    1. 9.1 Layout Guidelines
    2. 9.2 Layout Example
  11. 10Device and Documentation Support
    1. 10.1 Device Support
      1. 10.1.1 Third-Party Products Disclaimer
    2. 10.2 Documentation Support
      1. 10.2.1 Related Documentation
    3. 10.3 Receiving Notification of Documentation Updates
    4. 10.4 Support Resources
    5. 10.5 Trademarks
    6. 10.6 Electrostatic Discharge Caution
    7. 10.7 Glossary
  12. 11Revision History
  13. 12Mechanical, Packaging, and Orderable Information

6.3.3 Soft Start

The device has a soft-start feature that starts the device typically with 500-mA peak current limit until VO = 1.8 V and 500 µs elapsed when the input current limit is set to unlimited (see Section 6.3.4). Afterward, the output voltage ramps in a series of discrete steps (see Figure 6-6).

  • When VO ≤ 1.8 V, peak current is limited to 500 mA typical for 500 µs.
  • When VO > 1.8 V, each step is 100 mV high and has a duration of 125 µs.

The total soft-start ramp-up time can be calculated with Equation 2.

Equation 2. TPS63901

where

  • tr(SS) is the rise time of the output voltage in milliseconds.
  • VO is the output voltage in volts.

Figure 6-6 shows a typical start-up case.

TPS63901 Start-Up BehaviorFigure 6-6 Start-Up Behavior

Figure 6-7 illustrates the start-up step size behavior.

TPS63901 Typical Soft-Start Ramp Step SizeFigure 6-7 Typical Soft-Start Ramp Step Size

Table 6-1 shows the typical start-up time for a number of standard output voltages.

Table 6-1 Typical Start-Up Times
Output VoltageSoft-Start Ramp-Up Time (tr(SS))Start-Up Time (td(EN) + tr(SS))
1.8 V0.5 ms2 ms
2.5 V1.375 ms2.875 ms
3.3 V2.375 ms3.875 ms
5 V4.5 ms6 ms

If the output is prebiased – that is, the initial output voltage is not zero – the start-up behavior is as follows:

  • If the prebias voltage is lower than the target voltage, the device does not start switching until the ramping output voltage is greater than the prebias voltage (see Figure 6-8).
  • If the prebias voltage is higher than the target voltage, the device does not start to switch until the output voltage has decreased to the target voltage (see Figure 6-9). The device cannot actively discharge the output to the target voltage and relies on the load current to discharge the output capacitor and decrease the output voltage to the target value.
TPS63901 Start-Up Behavior into Prebiased (Low) OutputFigure 6-8 Start-Up Behavior into Prebiased (Low) Output
TPS63901 Start-Up Behavior into Prebiased (High) OutputFigure 6-9 Start-Up Behavior into Prebiased (High) Output