SNIU028D February 2016 – September 2020 UCD3138 , UCD3138064 , UCD3138064A , UCD3138128 , UCD3138A , UCD3138A64
In Resonant LLC topology, three modes are used. At the lowest power, a pulse width modulated mode (Multi Mode) is used. As power increases and frequency decreases, Resonant mode is used. As the frequency gets still lower, resonant mode is still used, however the Sync FET driver changes so that the on-time is fixed and does not increase (SR Pulse Width is clamped). Here are the waveforms for the LLC: