SLUP413A May   2024  – April 2026 TPS53689T

 

  1.   1
  2.   Abstract
  3. 1 Introduction
  4. 2 Converter Transient Response
  5. 3 Magnetics
  6. 4 TLVR Topology Operating Principles
    1. 4.1 Steady-State Operation
    2. 4.2 Load Transient Step-Up
    3. 4.3 Load Transient Step-Down
    4. 4.4 LC Inductor Selection
    5. 4.5 Steady-State Ripple
  7. 5 Power Loss and Efficiency
  8. 6 Phase Multiplication
  9. 7 PCB Layout
  10. 8 TLVR-Optimized Components
  11. 9 Example Side-by-Side Design
  12. 10Summary
  13. 11Additional Resources

4.3 Load Transient Step-Down

Figure 15 and Figure 16 show a simulated comparison between a multiphase buck converter and a TLVR design under the same load step-down condition. This simulation uses the same parameters as those in Table 2.

A few observations about Figure 15 and Figure 16:

  • The TLVR design responds to the transient (ISUM catches up to ILOAD) much more quickly because the ISUM is falling at a faster rate. As a consequence, the output voltage deviation is significantly lower.
  • In this case, both designs had the same number of phases off, but the TLVR design ramped down the ISUM at a faster rate.
Multiphase buck converter.Figure 15 Multiphase buck converter.
TLVR.Figure 16 TLVR.

Again, the relationship of ILC to ISUM explains the superior transient response of the TLVR design. And again, all inductors in the system follow the fundamental inductor relationship. During the transient response to the load step-down, the converter turns off all phases, NTOTAL, simultaneously. Equation 19 shows the falling ISUM slope for the multiphase buck converter:

Equation 19. ↓   S l o p e b u c k = – N T O T A L V O U T L

Using a similar analysis, Equation 20 shows the falling ISUM slope for the TLVR design, assuming that the TLVR magnetizing inductance LM is equal to the buck filter inductor L for comparison purposes. The TLVR design ramps down its ISUM faster given the factor from the LC loop, which decreases proportionally to the square of the number of phases, NTOTAL.

Equation 20. ↓ S l o p e T L V R ≅ ↓ S l o p e b u c k – N T O T A L   × N T O T A L ×   V O U T L C