SLVSFQ6A November   2020  – June 2021 TPS2640

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison
  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 Parameter 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 Undervoltage Lockout (UVLO)
      2. 9.3.2 Overvoltage Protection (OVP)
      3. 9.3.3 Reverse Input Supply Protection
      4. 9.3.4 Hot Plug-In and In-Rush Current Control
      5. 9.3.5 Overload and Short Circuit Protection
        1. 9.3.5.1 Overload Protection
          1. 9.3.5.1.1 Active Current Limiting
          2. 9.3.5.1.2 Electronic Circuit Breaker with Overload Timeout, MODE = OPEN
        2. 9.3.5.2 Short Circuit Protection
          1. 9.3.5.2.1 Start-Up With Short-Circuit On Output
        3. 9.3.5.3 FAULT Response
          1. 9.3.5.3.1 Look Ahead Overload Current Fault Indicator
        4. 9.3.5.4 Current Monitoring
        5. 9.3.5.5 IN, OUT, RTN, and GND Pins
        6. 9.3.5.6 Thermal Shutdown
        7. 9.3.5.7 Low Current Shutdown Control (SHDN)
    4. 9.4 Device Functional Modes
  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 Undervoltage Lockout and Overvoltage Set Point
        3. 10.2.2.3 Programming Current Monitoring Resistor—RIMON
        4. 10.2.2.4 Setting Output Voltage Ramp Time—(tdVdT)
          1. 10.2.2.4.1 Case 1: Start-Up Without Load—Only Output Capacitance C(OUT) Draws Current During Start-Up
          2. 10.2.2.4.2 Case 2: Start-Up With Load—Output Capacitance C(OUT) and Load Draws Current During Start-Up
          3. 10.2.2.4.3 Support Component Selections—RFLTb and C(IN)
      3. 10.2.3 Application Curves
    3. 10.3 System Examples
      1. 10.3.1 Acive ORing Operation
      2. 10.3.2 Field Supply Protection in PLC, DCS I/O Modules
      3. 10.3.3 Simple 24-V Power Supply Path Protection
    4. 10.4 Do's and Dont's
  11. 11Power Supply Recommendations
    1. 11.1 Transient Protection
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Device Support
    2. 13.2 Documentation Support
      1. 13.2.1 Related Documentation
    3. 13.3 Receiving Notification of Documentation Updates
    4. 13.4 Support Resources
    5. 13.5 Trademarks
    6. 13.6 Electrostatic Discharge Caution
    7. 13.7 Glossary
  14. 14Mechanical, Packaging, and Orderable Information
10.2.2.4.2 Case 2: Start-Up With Load—Output Capacitance C(OUT) and Load Draws Current During Start-Up

When the load draws current during the turnon sequence, additional power is dissipated in the device. Considering a resistive load RL(SU) during start-up, typical ramp-up of output voltage, load current and the instantaneous power dissipation in the device are shown in Figure 10-4. Instantaneous power dissipation with respect to time is plotted in Figure 10-5. The additional power dissipation during start-up is calculated using Equation 16.

GUID-20200603-SS0I-SPPX-MBL2-RWVHNBMJ2JW0-low.png

VIN = 24 V

CdVdT = 2.2 μF

RL(SU) = 48 Ω

COUT = 2.2 mF

Figure 10-4 Start-Up With Load
GUID-20200603-SS0I-WXLJ-5V03-0GZSJT87H7LG-low.gif

VIN = 24 V

CdVdT = 2.2 μF

RL(SU) = 48 Ω

COUT = 2.2 mF

Figure 10-5 PD(INRUSH) Due to Inrush and Load Current
Equation 16. GUID-20200603-SS0I-4VQT-NCCP-P491LPB3MRTL-low.gif

Total power dissipated in the device during start-up is given by Equation 17.

Equation 17. PD(STARTUP) PD(INRUSH) = PD(LOAD)

Total current during start-up is given by Equation 18.

Equation 18. I(STARTUP) = I(INRUSH) ÷ IL( t )

For the design example under discussion,

Select the inrush current I(INRUSH) = 0.1 A and calculate tdVdT using Equation 19.

Equation 19. GUID-20200603-SS0I-CLXN-1KVR-RVG711CBNVRX-low.gif

For a given start-up time, CdVdT capacitance value is calculated using Equation 20.

Equation 20. GUID-20200603-SS0I-TBKX-QB5Z-NRWHNDKRDX0Z-low.gif

where

  • t(dVdT) = 0.528 s
  • V(IN) = 24 V

Choose the closest standard value: 2.2-μF/16-V capacitor.

The inrush power dissipation is calculated, using Equation 21.

Equation 21. PD(INRUSH) = 0.5 × V(IN) = I(INRUSH) 1.2W

where

  • V(IN) = 24 V
  • I(INRUSH) = 0.1 A

Considering the start-up with 48-Ω load, the additional power dissipation, is calculated using Equation 22.

Equation 22. GUID-20200603-SS0I-T7KQ-CTLT-77RHVDN4MV4G-low.gif

where

  • V(IN) = 24 V
  • RL(SU) = 48 Ω

The total device power dissipation during start-up is given by Equation 23.

Equation 23. PD(STARTUP) = PD(INRUSH) + PD(LOAD) = 3.2W

where

  • PD(INRUSH) = 1.2 W
  • PD(LOAD) = 2 W

The power dissipation with or without load, for a selected start-up time must not exceed the thermal shutdown limits as shown in Figure 10-6 .

From the thermal shutdown limit graph, at TA = 85°C, thermal shutdown time for 3.2 W is close to 28000 ms. It is safe to have a minimum 30% margin to allow for variation of the system parameters such as load, component tolerance, input voltage and layout. Selected 2.2-μF CdVdT capacitor and 528-ms start-up time (tdVdT) are within limit for successful start-up with 48-Ω load.

Higher value C(dVdT) capacitor can be selected to further reduce the power dissipation during start-up.

GUID-20200604-SS0I-JDLZ-DPW3-0WT91VSFDJND-low.gif Figure 10-6 Thermal Shutdown Time vs Power Dissipation