Digital PWM for Multi-Level Flying Capacitor Converters with Improved Output Resolution and Flying Capacitor Voltage Controller Stability

This paper presents a flying capacitor voltage stability analysis comparing Trailing Edge (sawtooth counter) and Dual Edge (triangular counter) Digital Pulse-Width Modulation (DPWM) schemes when used on Multi-Level Flying Capacitor (ML-FC) converters, and shows that dual edge DPWM provides better stability for the flying capacitor voltage. Moreover, it presents a new, sawtooth counter based, Emulated Dual Edge DPWM scheme, that provides the same stability advantage and at the same time also has better digital pulse-width resolution than a typical triangular counter based Dual Edge DPWM. The introduced Emulated Dual Edge DPWM scheme allows the use of a simple linear compensator control scheme for the flying capacitor voltage of ML-FC converters, for the full range of operation, solving feedback instability issues that would arise with the use of trailing edge DPWM under light load operation. The introduced Emulated Dual Edge DPWM scheme was verified on a 20 W, 500 kHz, 12V-to-5V, Three-Level Flying Capacitor (3L-FC) buck converter, showing the stability of the flying capacitor control loop under light load operation and improved resolution, demonstrating its superiority over both the Trailing Edge and Dual Edge DPWM.

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