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UCC28950/about phase-shifted interleave

Tsukui Yusuke
Guru 21930 points

Other Parts Discussed in Thread: UCC28950

Hi,

Could you tell me about UCC28950 phase shift.
There is the following description in the data sheet page 26.
When I think from the master side,
The pattern that slave side becomes 180˚ delayed versus Master’s CLK or
90˚ delayed versus output switching pulses of Master.
Is there a way to fix this phase to one?
Customers want to fix the phase either.
Could you tell me if such as a circuit example.

◇Datasheet page 26
The UCC28950 allows flexible configuration of converters operating in synchronized mode by connecting all
SYNC pins together and by configuration of the controllers as master and/or slaves. The controller configured as
Master (resistor between RT and VREF) provides synchronization pulses at the SYNC pin with the frequency
equal to 2X the converter frequency FSW(nom) and 0.5 duty cycle. The controller configured as a Slave (resistor
between RT and GND and 825-kΩ resistor between SS_EN pin to GND) does not generate the synchronization
pulses. The Slave controller synchronizes its own clock to the falling edge of synchronization signal thus
operating 90° phase shifted versus the master converter’s frequency FSW(nom). Because the Slave is
synchronized to the falling edge of the SYNC pulses, the slave operates at 180˚ delayed versus Master’s CLK or
90˚ delayed versus output switching pulses of Master.

Best Regards,
Yusuke/Japan Disty

  • 0
    TI__Mastermind 25570 points

    Hello Yusuke-san

    The slave operates at 90deg from the master if you look at the transformer primary waveforms. In a full bridge converter the output inductor sees twice the switching frequency of the transformer primary so 90deg on the primary is equivalent to 180deg at the output inductor. The switching ripple on the output inductors will be 180 deg out of phase with each other. 

    The datasheet is a little unclear on this point - we are in the process of updating it.

    Is there a way to fix this phase to one?   Not in the device itself. The application note slua609 gives some ideas about how an external circuit could be used to fix any arbitrary phase between master and slave - although it does concentrate on 3 and 4 UCC28950s and setting the phase for maximum ripple cancellation.
    Customers want to fix the phase either.  - I'm not sure what you mean by this -
    Could you tell me if such as a circuit example. - the application note slua609 should give some information  - I don't have anything more.

    Regards

    Colin