SLVSEG3E September   2019  – March 2022 TPS25840-Q1 , TPS25842-Q1

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Description (Continued)
  6. 6 Device Comparison Table
  7. 7 Pin Configuration and Functions
  8. 8 Specifications
    1. 8.1 Absolute Maximum Ratings
    2. 8.2 ESD Ratings
    3. 8.3 Recommended Operating Conditions
    4. 8.4 Thermal Information
    5. 8.5 Electrical Characteristics
    6. 8.6 Timing Requirements
    7. 8.7 Switching Characteristics
    8. 8.8 Typical Characteristics
  9. 9 Parameter Measurement Information
  10. 10Detailed Description
    1. 10.1 Overview
    2. 10.2 Functional Block Diagram
    3. 10.3 Feature Description
      1. 10.3.1  Buck Regulator
      2. 10.3.2  Enable/UVLO
      3. 10.3.3  Switching Frequency and Synchronization (RT/SYNC)
      4. 10.3.4  Spread-Spectrum Operation
      5. 10.3.5  VCC, VCC_UVLO
      6. 10.3.6  Minimum ON-time, Minimum OFF-time
      7. 10.3.7  Internal Compensation
      8. 10.3.8  Bootstrap Voltage (BOOT)
      9. 10.3.9  RSNS, RSET, RILIMIT and RIMON
      10. 10.3.10 Overcurrent and Short Circuit Protection
        1. 10.3.10.1 Current Limit Setting using RILIMIT
        2. 10.3.10.2 Buck Average Current Limit Design Example
        3. 10.3.10.3 External MOSFET Gate Drivers
        4. 10.3.10.4 Cycle-by-Cycle Buck Current Limit
      11. 10.3.11 Overvoltage, IEC and Short-to-Battery Protection
        1. 10.3.11.1 V BUS and V CSN/OUT Overvoltage Protection
        2. 10.3.11.2 DP_IN and DM_IN Protection
      12. 10.3.12 Cable Compensation
        1. 10.3.12.1 Cable Compensation Design Example
      13. 10.3.13 USB Port Control
      14. 10.3.14 FAULT Response
      15. 10.3.15 USB Specification Overview
      16. 10.3.16 Device Power Pins (IN, CSN/OUT, and PGND)
      17. 10.3.17 Thermal Shutdown
    4. 10.4 Device Functional Modes
      1. 10.4.1 Shutdown Mode
      2. 10.4.2 Active Mode
      3. 10.4.3 Device Truth Table (TT)
      4. 10.4.4 USB Port Operating Modes
        1. 10.4.4.1 Standard Downstream Port (SDP) Mode — USB 2.0, USB 3.0, and USB 3.1
        2. 10.4.4.2 Charging Downstream Port (CDP) Mode
        3. 10.4.4.3 Client Mode
      5. 10.4.5 High-bandwidth Data-line Switches
  11. 11Application and Implementation
    1. 11.1 Application Information
    2. 11.2 Typical Application
      1. 11.2.1 Design Requirements
      2. 11.2.2 Detailed Design Procedure
        1. 11.2.2.1  Output Voltage
        2. 11.2.2.2  Switching Frequency
        3. 11.2.2.3  Inductor Selection
        4. 11.2.2.4  Output Capacitor Selection
        5. 11.2.2.5  Input Capacitor Selection
        6. 11.2.2.6  Bootstrap Capacitor Selection
        7. 11.2.2.7  VCC Capacitor Selection
        8. 11.2.2.8  Enable and Under Voltage Lockout Set-Point
        9. 11.2.2.9  Current Limit Set-Point
        10. 11.2.2.10 Cable Compensation Set-Point
        11. 11.2.2.11 FAULT Resistor Selection
      3. 11.2.3 Application Curves
  12. 12Power Supply Recommendations
  13. 13Layout
    1. 13.1 Layout Guidelines
    2. 13.2 Ground Plane and Thermal Considerations
    3. 13.3 Layout Example
  14. 14Device and Documentation Support
    1. 14.1 Documentation Support
      1. 14.1.1 Related Documentation
    2. 14.2 Related Links
    3. 14.3 Receiving Notification of Documentation Updates
    4. 14.4 Support Resources
    5. 14.5 Trademarks
    6. 14.6 Electrostatic Discharge Caution
    7. 14.7 Glossary
  15. 15Mechanical, Packaging, and Orderable Information

Package Options

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

11.2.2.4 Output Capacitor Selection

The value of the output capacitor, and its ESR, determine the output voltage ripple and load transient performance. The output capacitor bank is usually limited by the load transient requirements, rather than the output voltage ripple. Equation 11 can be used to estimate a lower bound on the total output capacitance, and an upper bound on the ESR, required to meet a specified load transient.

Equation 11. GUID-80B1F6F9-DCDF-453E-BB64-B0F84AF053EB-low.gif

where

  • ΔVOUT = output voltage transient
  • ΔIOUT = output current transient
  • K = Ripple factor from Inductor Selection

After the output capacitor and ESR have been calculated, Equation 12 can be used to check the peak-to-peak output voltage ripple, Vr.

Equation 12. GUID-F8EA52B6-55EF-45F0-A8A0-FBE2B8CEE1E8-low.gif

The output capacitor and ESR can then be adjusted to meet both the load transient and output ripple requirements.

For this example, we require a ΔVOUT of ≤ 250 mV for an output current step of ΔIOUT = 2.7 A. Equation 11 gives a minimum value of 86 µF and a maximum ESR of 0.08 Ω. Assuming a 20% tolerance and a 10% bias de-rating, we arrive at a minimum capacitance of 110 µF. This can be achieved with a bank of 5 × 22-µF, 10-V, ceramic capacitors in the 1210 case size. More output capacitance can be used to improve the load transient response. Ceramic capacitors can easily meet the minimum ESR requirements. In some cases an aluminum electrolytic capacitor can be placed in parallel with the ceramics to help build up the required value of capacitance.

In practice, the output capacitor has the most influence on the transient response and loop phase margin. Load transient testing and Bode plots are the best way to validate any given design and must always be completed before the application goes into production. In addition to the required output capacitance, a small ceramic placed on the output can help to reduce high frequency noise. Small case size ceramic capacitors in the range of 1 nF to 100 nF can be very helpful in reducing voltage spikes on the output caused by inductor and board parasitics.

The maximum value of total output capacitance must be limited to about 10 times the design value, or 1000 µF, whichever is smaller. Large values of output capacitance can adversely affect the start-up behavior of the regulator as well as the loop stability. If values larger than noted here must be used, then a careful study of start-up at full load and loop stability must be performed.