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Original question:

UCC28064A: About using only in single phase

UCC28064A: About using in single mode

kiri yasuda
Prodigy 30 points
Part Number: UCC28064A

Tool/software:

Hello.

We have designed a UCC28064A board in interleaved mode, but our customer wants a single mode design on the same board.

The question is similar to the previous forum attached. The answer is that running in single mode forces dual mode at startup, but what specific problems do you experience when using the UCC28064A to start the circuit in single mode?

Also, does the problem occur outside of startup?

Can you provide support on the forum when I run the circuit in single mode using the UCC28064A and encounter problems?

Thanks.

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/738673/ucc28064a-about-using-only-in-single-phase?tisearch=e2e-sitesearch&keymatch=UCC28064A#

  • 0
    TI__Mastermind 33330 points

    Hello Yasuda-san, 

    To run the UCC28064A in single-phase mode continuously, connect the PHB input to VREF.  This will disable Phase-B gate-drive at all times, except at start-up. 

    This specific operating mode was designed into the controller in order to minimize the possible amount of CCM current in the inductor(s) when starting up at the maximum high-line input voltage.   Normally, it is expected that two phases are used with this device.  When starting at the peak of high line, the output voltage is close to the input peak and the inductor current may not demagnetize all the way to 0A before the next switching cycle is started.  For a few cycles, a small amount of CCM current may build up until the output voltage exceeds the input voltage by several volts.  Then normal transition mode current is established. 

    When operating in single-phase-mode (Vcomp < Vphb), the on-time per cycle is automatically doubled.  If single-phase operation is active at start-up, the longer on-time may allow higher CCM to build up.  To minimize CCM at start-up, the controller over-rides single-phase mode (only at start-up) in order to reduce the available on-time for the gate-drives.  

    If you connect PHB to VREF to force 1-phase all the time, GDB will still be drive (only at start-up) but if no switching components are populated on the board, then there will be no effect from the GDB signal. However, GDA will start up switching at 1/2 of the on-time that it will have after start-up is completed, so start-up time may be slower than if 2-phases were active. 

    Lastly, since the IC expects Phase-B to be active at start-up, but there is no Phase-B circuit, there will be no ZCDB signals.  The controller may construe the lack of ZCDB signals as a Phase-Fault.  The action of a Phase-Fault in the UCC28064A is to reduce the peak current limit threshold at the CS input to -0.166V (down from -0.200V).  There will be no other action.  
    After start-up is complete, the Phase-B path will be disabled and the Phase-Fault will be cancelled.  Single-phase operation will begin and the CS peak limit will continue at -0.166V threshold. 

    If you encounter problems running the UCC28064A in single-phase mode or any other mode, TI can support you through this forum to solve them.

    Regards,
    Ulrich