SPRUJ53B April 2024 – September 2024 TMS320F28P550SJ , TMS320F28P559SJ-Q1
The example given in Figure 19-72 assumes a static or constant phase relationship between legs (modules). In such a case, control is achieved by modulating the duty cycle. It is also possible to dynamically change the phase value on a cycle-by-cycle basis. This feature lends to controlling a class of power topologies known as phase-shifted full bridge, or zero voltage switched full bridge. Here the controlled parameter is not duty cycle (this is kept constant at approximately 50 percent); instead it is the phase relationship between legs. Such a system can be implemented by allocating the resources of two PWM modules to control a single power stage, which in turn requires control of four switching elements. Figure 19-73 shows a sync source and sync receiver module combination synchronized together to control a full H-bridge. In this case, both sync source and sync receiver modules are required to switch at the same PWM frequency. The phase is controlled by using the sync receiver phase register (TBPHS). The sync source phase register is not used and therefore can be initialized to zero.