UCC28064A: Question about Paralleling two UCC28064A

Hello,

There is an error in this application note in the schematic title in figure 2-1.  The control devices is a transition mode PFC controllers (UCC28064A) devices and not CCM controller (UCC28070).

I reviewed the application note.  If you follow the application note the UCC28064A the 4 phases will not be operating 90 degrees out of phase from each other.

The converter controls two interleaved boost converters (S1,S2).  The two stages and share a common control voltage and will ensure through constant on time control that peak current of the boost stages are equal during each switching cycle.  Phase A and B of S1 will operate with 180 degree phase from each other and will not be synchronized with S2.  Phase A and B of S2 will operate at 180 degree phase shift from each other but will not be synchronized with S1.

The UCC28064A synchronizes two transition mode PFC stages that are frequency modulated internally to the controller.  There is not a way to synchronize two UCC28064A controllers with a 90 degree phase shift between the phases.

There are benefits of interleaving with the 90 degree phase shift with inductor ripple current cancelation and capacitor RMS current reduction.  The application note I believe does mention this.  However, that is not possible using the UCC28064A.  The UCC28070/A average current mode PFC controllers do have an external sync input.  It is possible with external synchronization circuitry to synchronize two UCC28070/A controllers so the are outputs are 90 degrees out of phase.  The following link will bring you to the data sheet of the UCC28070/A controllers if you are interested. 

https://www.ti.com/lit/ds/symlink/ucc28070.pdf

Regards,

Hello,

The UCC28064A was designed for 800 W and should be able to handle 820 W.  This would be an interleaved PFC with two phases.

You could parallel two, two  phase interleaved PFC stages as the application not previously mentioned using the UCC28064A recommends.  Please note that the two phases will be free running and requires more components.  The benefit of doing this is higher efficiency and more complex design.

In your case since the power level is low enough, I would recommend using one UCC28064A controlling two boost phases.  If you were doing a 1600 W paralleling two, two phase interleaved would be a better a choice.

Regards,