SLVSCE1C August   2014  – November 2015 TPS25921A , TPS25921L


  1. Features
  2. Applications
  3. Description
  4. Application Schematic
  5. Revision History
  6. Pin Configuration and Functions
  7. Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Characteristics
    5. 7.5 Electrical Characteristics
    6. 7.6 Timing Requirements
    7. 7.7 Typical Characteristics
  8. Parametric Measurement Information
  9. Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Enable and Adjusting Undervoltage Lockout (UVLO)
      2. 9.3.2 Overvoltage Protection (OVP)
      3. 9.3.3 Hot Plug-in and In-Rush Current Control
      4. 9.3.4 Overload and Short Circuit Protection :
        1. Overload Protection
        2. Short Circuit Protection
        3. Start-Up with Short on Output
        4. Constant Current Limit Behavior during Overcurrent Faults
      5. 9.3.5 FAULT Response
      6. 9.3.6 IN, OUT and GND Pins
      7. 9.3.7 Thermal Shutdown:
    4. 9.4 Device Functional Modes
      1. 9.4.1 Shutdown Control
      2. 9.4.2 Operational Overview of Device Functions
  10. 10Applications and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Precision Current Limiting and Protection for White Goods
        1. Design Requirements
        2. Detailed Design Procedure
          1. Step by Step Design Procedure
          2. Programming the Current-Limit Threshold: R(ILIM) Selection
          3. Undervoltage Lockout and Overvoltage Set Point
          4. Setting Output Voltage Ramp time (tSS)
            1. Case1: Start-up Without Load: Only Output Capacitance C(OUT) Draws Current During Start-up
            2. Case 2: Start-up With Load: Output Capacitance C(OUT) and Load Draws Current During Start-up
          5. Support Component Selections - R4 and CIN
        3. Application Curves
    3. 10.3 System Examples
      1. 10.3.1 Protection and Current Limiting for Primary-Side Regulated Power Supplies
      2. 10.3.2 Precision Current Limiting in Intrinsic Safety Applications
      3. 10.3.3 Smart Load Switch
  11. 11Power Supply Recommendations
    1. 11.1 Transient Protection
    2. 11.2 Output Short-Circuit Measurements
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Related Links
    2. 13.2 Community Resources
    3. 13.3 Trademarks
    4. 13.4 Electrostatic Discharge Caution
    5. 13.5 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

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

11 Power Supply Recommendations

The device is designed for supply voltage range of 4.5 V ≤ VIN ≤ 18 V. If the input supply is located more than a few inches from the device an input ceramic bypass capacitor higher than 0.1 μF is recommended. Power supply should be rated higher than the current limit set to avoid voltage droops during over current and short-circuit conditions.

11.1 Transient Protection

In case of short circuit and over load current limit, when the device interrupts current flow, input inductance generates a positive voltage spike on the input and output inductance generates a negative voltage spike on the output. The peak amplitude of voltage spikes (transients) is dependent on value of inductance in series to the input or output of the device. Such transients can exceed the Absolute Maximum Ratings of the device if steps are not taken to address the issue.

Typical methods for addressing transients include

  • Minimizing lead length and inductance into and out of the device
  • Using large PCB GND plane
  • Schottky diode across the output to absorb negative spikes
  • A low value ceramic capacitor (C(IN) = 0.001 µF to 0.1 µF) to absorb the energy and dampen the transients. The approximate value of input capacitance can be estimated with Equation 31.
Equation 31. TPS25921A TPS25921L eq_43_slvsce9.gif


  • V(IN) is the nominal supply voltage
  • I(LOAD) is the load current,
  • L(IN) equals the effective inductance seen looking into the source
  • C(IN) is the capacitance present at the input
Some applications may require the addition of a Transient Voltage Suppressor (TVS) to prevent transients from exceeding the Absolute Maximum Ratings of the device.

The circuit implementation with optional protection components (a ceramic capacitor, TVS and schottky diode) is shown in Figure 51.

TPS25921A TPS25921L Circuit_Implementation_slvsce1.gif
1. Optional components needed for suppression of transients
Figure 51. Circuit Implementation With Optional Protection Components

11.2 Output Short-Circuit Measurements

It is difficult to obtain repeatable and similar short-circuit testing results. Source bypassing, input leads, circuit layout and component selection, output shorting method, relative location of the short, and instrumentation all contribute to variation in results. The actual short itself exhibits a certain degree of randomness as it microscopically bounces and arcs. Care in configuration and methods must be used to obtain realistic results. Do not expect to see waveforms exactly like those in the data sheet; every setup differs.