SLUAAR8 December   2023 TPS56837

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Review of CCM Output Voltage Ripple in Buck Converter
  5. 2Calculation of DCM Output Voltage Ripple in D-CAP Buck Converter
  6. 3Bench Test Results and Error Analysis
    1. 3.1 Bench Test Results
    2. 3.2 Error Analysis
      1. 3.2.1 Variation in High-Side FET on Time
      2. 3.2.2 Variation in Component Value
  7. 4Comparison Between DCM and CCM Output Voltage Ripple in D-CAP Buck Converter
  8. 5Summary
  9. 6References

1 Review of CCM Output Voltage Ripple in Buck Converter

Output voltage ripple is a key parameter for buck converter, which could make great impact on system application and should be paid more attention on. The principle for generation of output voltage ripple for buck converter is well illustrated in many text books and application notes. A brief review of CCM output voltage ripple in buck converter will be given first.

For CCM operation, inductor current increases from its valley value at the beginning of switch cycle, reaching its peak value when high-side FET is OFF and going back to its valley value when the switch cycle is finished. The average inductor current is loading current.

When only considering impacts of output capacitors, output voltage ripple is raised by charging and discharging process of output capacitors. Excessive energy marked with Q1 in Figure 1-1 will be charged to COUT, leading to the rise of voltage on COUT. When the inductor current is lower than loading current, COUT will discharge to maintain VOUT stable. So output voltage ripple will be calculated by Equation 1 and Equation 2.

Equation 1. Q1=∆IL×TSW8
Equation 2. ∆VOUT=Q1COUT=∆IL×TSW8×COUT

Q1: Excessive energy

TSW: Switching period

ΔVOUT: Output voltage ripple

COUT: Value of output capacitors

GUID-20231210-SS0I-X0TV-QSGS-9VLS01CQ1CTW-low.svg Figure 1-1 Inductor Current Illustration for CCM Operation