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UCC256301: Hybrid Hysteretic Mode and Current Mode Controlled

Carlo Andres
Prodigy 40 points
Part Number: UCC256301

I'm having problem in understanding how hybrid hysteretic mode explanation in the datasheet. Specifically on the value of AVDD and how does it help. Also, how does the "added frequency compensation affects" and VCR on the feedback. 

  • 0
    TI__Mastermind 27145 points
    Hi Carlo,

    Thanks for your interest in UCC256301. Hybrid hysteretic mode control is a blend of charge control and direct frequency control.

    The current sourced into the FB pin is split between the optocoupler and RFB. The current flowing through RFB creates the FBreplica voltage. The FBreplica voltage is fed into a differential amplifier to create two thresholds: VTH and VTL. These two thresholds are symmetric around VCM (VCM is ~3V).

    The Vcr capacitor divider looks at the AC component of the resonant capacitor voltage. When the Vcr voltage is greater than VTH, the controller turns off the high side mosfet. When the Vcr voltage is less than VTL, the controller turns off the low side mosfet. This is the charge control portion of HHC.

    There is a current source and a current sink connected to the Vcr pin. The source and sink are turned on and off in conjunction with either the high side mosfet turning on or the low side mosfet turning on. This adds a triangular waveform to the Vcr pin. The is the direct frequency control portion of HHC (it's a frequency compensation ramp).

    By decreasing the capacitance in the Vcr divider, the frequency compensation ramp dominates the Vcr waveform and you see performance similar to direct frequency control. By increasing the capacitance in the Vcr divider, the AC component of the resonant capacitor dominates the Vcr waveform and you see performance similar to charge control.

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Prodigy 40 points

    Hi Ben Lough,

    Thanks for the discussion about it. Another question however not relared on the title. On the given SIMPLIS Model of the UCC256301, can I use POP Trigger in the simulation and where should I connect the perturbation so I can see the Bode Plot of it?

  • 0 in reply to Carlo Andres
    TI__Mastermind 27145 points

    Hi Carlo,

    Apologies for the delay.To use POP, connect the input of the POP symbol to LO (it looks for the periodic operating point). The output of the POP symbol can be left unconnected. Next, place an AC source with low magnitude between VOUT and the top of the feedback resistor divider. Then place a bode plot symbol in parallel with the AC source you inserted. Here is an example of POP with the UCC25630x simplis model. UCC25630x_SIMPLIS_for_Carlo.zip

    Best Regards,

    Ben Lough