SLUSEA4D June   2021  – August 2022 TPS62932 , TPS62933 , TPS62933F , TPS62933O , TPS62933P

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 Typical Characteristics
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1  Fixed Frequency Peak Current Mode
      2. 9.3.2  Pulse Frequency Modulation
      3. 9.3.3  Voltage Reference
      4. 9.3.4  Output Voltage Setting
      5. 9.3.5  Switching Frequency Selection
      6. 9.3.6  Enable and Adjusting Undervoltage Lockout
      7. 9.3.7  External Soft Start and Prebiased Soft Start
      8. 9.3.8  Power Good
      9. 9.3.9  Minimum On Time, Minimum Off Time, and Frequency Foldback
      10. 9.3.10 Frequency Spread Spectrum
      11. 9.3.11 Overvoltage Protection
      12. 9.3.12 Overcurrent and Undervoltage Protection
      13. 9.3.13 Thermal Shutdown
    4. 9.4 Device Functional Modes
      1. 9.4.1 Modes Overview
      2. 9.4.2 Heavy Load Operation
      3. 9.4.3 Light Load Operation
      4. 9.4.4 Out of Audio Operation
      5. 9.4.5 Forced Continuous Conduction Operation
      6. 9.4.6 Dropout Operation
      7. 9.4.7 Minimum On-Time Operation
      8. 9.4.8 Shutdown Mode
  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  Custom Design With WEBENCH® Tools
        2. 10.2.2.2  Output Voltage Resistors Selection
        3. 10.2.2.3  Choosing Switching Frequency
        4. 10.2.2.4  Soft-Start Capacitor Selection
        5. 10.2.2.5  Bootstrap Capacitor Selection
        6. 10.2.2.6  Undervoltage Lockout Setpoint
        7. 10.2.2.7  Output Inductor Selection
        8. 10.2.2.8  Output Capacitor Selection
        9. 10.2.2.9  Input Capacitor Selection
        10. 10.2.2.10 Feedforward Capacitor CFF Selection
        11. 10.2.2.11 Maximum Ambient Temperature
      3. 10.2.3 Application Curves
    3. 10.3 What to Do and What Not to Do
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Device Support
      1. 13.1.1 Third-Party Products Disclaimer
      2. 13.1.2 Development Support
        1. 13.1.2.1 Custom Design With WEBENCH® Tools
    2. 13.2 Receiving Notification of Documentation Updates
    3. 13.3 Support Resources
    4. 13.4 Trademarks
    5. 13.5 Electrostatic Discharge Caution
    6. 13.6 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

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

10.2.2.8 Output Capacitor Selection

The device is designed to be used with a wide variety of LC filters, so it is generally desired to use as little output capacitance as possible to keep cost and size down. Choose the output capacitance, COUT, with care since it directly affects the following specifications:

  • Steady state output voltage ripple
  • Loop stability
  • Output voltage overshoot and undershoot during load current transient

The output voltage ripple is essentially composed of two parts. One is caused by the inductor current ripple going through the Equivalent Series Resistance (ESR) of the output capacitors:

Equation 19. GUID-20210219-CA0I-VMRV-RMJK-NQLPNVNBTVV1-low.gif

The other is caused by the inductor current ripple charging and discharging the output capacitors:

Equation 20. GUID-20210219-CA0I-LWXZ-25HR-15VMHXCHQG95-low.gif

where

  • K is the ripple ratio of the inductor current (ΔIL / IOUT_MAX).

The two components in the voltage ripple are not in phase, so the actual peak-to-peak ripple is smaller than the sum of the two peaks.

Output capacitance is usually limited by the load transient requirements rather than the output voltage ripple if the system requires tight voltage regulation with presence of large current steps and fast slew rate. When a large load step happens, output capacitors provide the required charge before the inductor current can slew up to the appropriate level. The control loop of the converter usually needs eight or more clock cycles to regulate the inductor current equal to the new load level. The output capacitance must be large enough to supply the current difference for about eight clock cycles to maintain the output voltage within the specified range. Equation 21 shows the minimum output capacitance needed for specified VOUT overshoot and undershoot.

Equation 21. GUID-20210110-CA0I-KM0D-JRKW-9WCFCSFJMDQH-low.gif

where

  • D is VOUT / VIN, duty cycle of steady state.
  • ΔVOUT is the output voltage change.
  • ΔIOUT is the output current change.

For this design example, the target output ripple is 30 mV. Presuppose ΔVOUT_ESR = ΔVOUT_C = 30 mV and choose K = 0.4. Equation 19 yields ESR no larger than 25 mΩ and Equation 20 yields COUT no smaller than 10 μF. For the target overshoot and undershoot limitation of this design, ΔVOUT_SHOOT < 5% × VOUT = 250 mV for an output current step of ΔIOUT = 1.5 A. COUT is calculated to be no smaller than 25 μF by Equation 21. In summary, the most stringent criterion for the output capacitor is 25 μF. Considering the ceramic capacitor has DC bias de-rating, it can be achieved with a bank of 2 × 22-μF, 35-V, ceramic capacitor C3216X5R1V226M160AC in the 1206 case size.

More output capacitors 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 build up the required value of capacitance. When using a mixture of aluminum and ceramic capacitors, use the minimum recommended value of ceramics and add aluminum electrolytic capacitors as needed.

The recommendations given in Table 10-2 provide typical and minimum values of output capacitance for the given conditions. These values are the effective figures. If the minimum values are to be used, the design must be tested over all of the expected application conditions, including input voltage, output current, and ambient temperature. This testing must include both bode plot and load transient assessments. The maximum value of total output capacitance can be referred to COUT selection and CFF selection in the TPS62933 Thermal Performance with SOT583 Package Application Report. Large values of output capacitance can adversely affect the start-up behavior of the converter 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.

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 reduce high frequency noise. Small case size ceramic capacitors in the range of 1 nF to 100 nF can help reduce spikes on the output caused by inductor and board parasitics.

Table 10-2 shows the recommended LC combination.

Table 10-2 Recommended LC Combination for TPS62933
VOUT(V)fSW (kHz)RTOP(kΩ)RDOWN(kΩ)Typical Inductor L (μH)Typical Effective COUT (μF)Minimum Effective COUT (μF)
3.350031.310.04.74015
12002.23010
550052.510.06.82010
12003.32010
12500140.010.0121510