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UCC28740 current control

Max Power1
Prodigy 80 points
Other Parts Discussed in Thread: UCC28740

Hi,

I would use this controller for my application. From the datasheet it's not so clear how the current control is performed.

So, it's a bit hard the simulate it on tools like PSIM.

Could anyone help me, please?

  • 0
    TI__Expert 5900 points

    Hello Sir,

    What do you want to know about the Current control?

    If you want to know something about the constant current control, you can refer to the "Primary-Side Constant-Current (CC) Regulation" section in page 16 of the UCC28740 spec.

    Regards

  • 0 in reply to Kening Gao
    Prodigy 80 points

    Hello Sir,

    what I understood, reading the datasheet on page15 is:

    1. if output voltage increases, IFB increases and VCL decreases (VCL<=2.2V means that Vcs=Vcsmin) ;
    2. if output voltage decreases, IFB decreases and VCL increases (VCL>=3.5V means that Vcs=Vcsmax) ;

    Then, on page 16 this sentence appears

    "When the load current of the converter increases to the predetermined constant-current limit, operation enters
    CC mode."

    • Which is this limit? From page 15 it seems to be VCL=4.9V.
    • So, if this is true, I should design the feedback net in the way that nominal output voltage corresponds to VCL 4.9V? 
    • If output voltage decreases under nominal value, fsw diminishes too as it is specified on page 16? 
    • In CC regulation, the VCST value is constant and equal to VCSTmax?

    On the other hand, taking a look at page 6 (functional diagram block),  Ivls/KLC adds to the current sensing signal. Is this signal the current control ramp? How do I consider this signal in the overall control network?

    Thanks,