The typical way of achieving LLC control in MCU is to implement a control loop with fixed frequency, so that the interrupts and background loops can all be well organized and responded correctly. However, since the LLC switching frequency is changing from cycle to cycle, the timing relationship between switching and control ISR becomes unpredictable.

Traditionally, shadow register is loaded as active whenever the event configured happens. And in type-4 PWM it can be CTR=PRD, CTR-Zero and, and so forth. Thus, in LLC converter it is important to ensure PWM configuration is carefully updated at the beginning or ending of a PWM switch cycle, to guarantee it does not cause any PWM disorder. Ideally the shadow to active load should be forbidden when PWM configuration update happens, so duty cycle, period and phase shift mismatch would not happen.

To solve this problem, one shot load is introduced in C2000 type-4 ePWM. The idea is to add an additional ‘mask’ to the shadow to active load event. The shadow to active load will only be trigger by the load event when GLDCTL2[OSHTLD] is set as 1, and this bit will be cleared automatically once a load happens, to get ready for the next update.