SLVSDJ0E May   2016  – January 2021 TPS25940-Q1

PRODMIX  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Timing Requirements
    7. 7.7 Typical Characteristics
  8. 8 Parametric Measurement Information
  9. 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
      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. 9.3.4.1 Overload Protection
        2. 9.3.4.2 Short Circuit Protection
        3. 9.3.4.3 Start-Up with Short on Output
        4. 9.3.4.4 Constant Current Limit Behavior During Overcurrent Faults
      5. 9.3.5 FAULT Response
      6. 9.3.6 Current Monitoring
      7. 9.3.7 Power Good Comparator
      8. 9.3.8 IN, OUT and GND Pins
      9. 9.3.9 Thermal Shutdown
    4. 9.4 Device Functional Modes
      1. 9.4.1 DevSleep Mode
      2. 9.4.2 Shutdown Control
  10. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. 10.2.2.1 Step by Step Design Procedure
        2. 10.2.2.2 Programming the Current-Limit Threshold: R(ILIM) Selection
        3. 10.2.2.3 Undervoltage Lockout and Overvoltage Set Point
        4. 10.2.2.4 Programming Current Monitoring Resistor—RIMON
        5. 10.2.2.5 Setting Output Voltage Ramp Time (tdVdT)
          1. 10.2.2.5.1 Case1: Start-Up Without Load: Only Output Capacitance C(OUT) Draws Current During Start-Up
          2. 10.2.2.5.2 Case 2: Start-Up With Load: Output Capacitance C(OUT) and Load Draws Current During Start-Up
        6. 10.2.2.6 Programing the Power Good Set Point
        7. 10.2.2.7 Support Component Selections—R6, R7 and CIN
      3. 10.2.3 Application Curves
      4. 10.2.4 System Examples
        1. 10.2.4.1 VBUS Short-to-Battery, Short-to-Ground Protection of USB Port in Automotive Systems
        2. 10.2.4.2 Power Failure Protection for Holdup Power
        3. 10.2.4.3 Overload Detection Using TPS25940xx-Q1
  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 Documentation Support
      1. 13.1.1 Related Documentation
    2. 13.2 Support 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

10.2.2.3 Undervoltage Lockout and Overvoltage Set Point

The undervoltage lockout (UVLO) and overvoltage trip point are adjusted using the external voltage divider network of R1, R2 and R3 as connected between IN, EN, OVP and GND pins of the device. The values required for setting the undervoltage and overvoltage are calculated solving Equation 10 and Equation 11.

Equation 10. GUID-2367E398-1EAD-4143-AB75-54646B39ADFA-low.gif
Equation 11. GUID-A70D04BD-C7C8-4EDB-8B5B-137FDEC4651D-low.gif

For minimizing the input current drawn from the power supply {I(R123) = V(IN)/(R1 + R2 + R3)}, it is recommended to use higher values of resistance for R1, R2 and R3.

However, leakage currents because of the external active components connected to the resistor string can add error to these calculations. So, the resistor string current, I(R123) must be chosen to be 20 times greater than the leakage current expected.

From the device electrical specifications, V(OVPR) = 0.99 V and V(ENR) = 0.99 V. For design requirements, V(OV) is 16.5 V and V(UV) is 10.8 V. To solve the equation, first choose the value of R3 = 31.2 kΩ and use Equation 10 to solve for (R1 + R2) = 488.8 kΩ. Use Equation 11 and value of (R1 + R2) to solve for R2 = 16.47 kΩ and finally R1= 472.33 kΩ.

Using the closest standard 1% resistor values gives R1 = 475 kΩ, R2 = 16.7 kΩ, and R3 = 31.2 kΩ.

The power failure threshold is detected on the falling edge of supply. This threshold voltage is 7% lower than the rising threshold, V(UV). This is calculated using Equation 12.

Equation 12. V(PFAIL) = 0.93 x V(UV)