SDAA195 January   2026 LMG3522R030

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Operating Principles in a Flying Capacitor Switching Cell
    1. 2.1 Switching Pattern of a 3-Level Flying Capacitor Switching Cell
  6. 3Design Considerations of a Flying Capacitor Switching Cell
    1. 3.1 Conduction and Switching Losses
      1. 3.1.1 AC Conduction Losses
      2. 3.1.2 AC Switching Losses
    2. 3.2 Passive Components Design
      1. 3.2.1 Boost Inductor Design
      2. 3.2.2 DC Link High Frequency Ripple
      3. 3.2.3 Flying Capacitor Design
    3. 3.3 Layout Considerations
    4. 3.4 Pre-Charging Network
  7. 4Experimental Results
    1. 4.1 Pre-charging of the Flying Capacitor of TIDA-010957
    2. 4.2 Steady State Operation
  8. 5Summary
  9. 6References

2 Operating Principles in a Flying Capacitor Switching Cell

Three-Level Flying Capacitor Switching Cell Figure 2-1 Three-Level Flying Capacitor Switching Cell

In a three-level switching cell, the following components can be found as shown in Figure 2-1:

  • S1, S2, S3 and S4 are four power switches.
  • CFC is the flying capacitor.
  • LSW is the switching node inductance.
  • CDC is the DC link voltage capacitor.

Note that this topology is considered a boost converter topology, where the VSW voltage is always lower than the DC link voltage (VDC).

In this topology, the three voltage levels on the switching node output are achieved by turning the transistors on with the right combination:

  1. Output equal to Vdc: S1 and S2 are ON.
  2. Output equal to 0 V: S3 and S4 are ON.
  3. Output equal to V_DC-V_FC: S1 and S3 ON.
  4. Output equal to V_FC: S2 and S4 ON.

As can be seen from the third and fourth switching states, it is important to control the voltages of the two capacitors constant (Vfc and Vdc). This condition makes sure that the switching node voltage is half the DC link voltage, if the flying capacitor voltage is control to half the DC link voltage.