SNIU028D February 2016 – September 2020 UCD3138 , UCD3138064 , UCD3138064A , UCD3138128 , UCD3138A , UCD3138A64
The resonant mode operation depends on the status of the RESON_DEADTIME_COMP_EN bit. Setting the RESON_DEADTIME_COMP_EN bit provides for a symmetrical waveform where DPWMA and DPWMB have the same pulse width. As the switching frequency changes, the dead times between the pulses remain the same. This mode is ideal for the LLC topology.
Clearing the RESON_DEADTIME_COMP_EN bit provides a mode where the pulse widths are the same and the duty cycle percentage is constant as the period changes. This means that as the frequency increases, the dead times shrink proportionally.
The equations for this mode are designed for a smooth transition from PWM mode to Resonant mode, as described in Section 2.11.1. Here is a diagram of this mode:
As seen later, the Filter module has two outputs, Filter Duty and Filter Period. In the Resonant mode, the Filter is configured so that the Filter Period is twice the Filter Duty. With zero dead times, each DPWM pin would be On for half of the period. For dead time handling, the average of the two dead times is subtracted from the Filter Duty for both DPWM pins. Therefore both pins will have the same on-time, and the dead times will be fixed regardless of the period. The only edge which is fixed relative to the start of the period is the rising edge of DPWM A. Blanking A and Blanking B both work only on DPWMA.