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UCC28780: Design support

Sirui Zhu
Intellectual 2090 points
Part Number: UCC28780
Other Parts Discussed in Thread: UCC24612, UCC24650, UCC2897A

Hi team,

My customer has following questions on this chip:

1.Is UC28780 suitable to control the active dual-position flyback chip to be used in a 70W 24/24V isolated dcdc circuit (the upper and the lower switch are MOS tubes with Vgs(th)=4V)
2.In the case of inputting 24V±20%, can the auxiliary winding on the VDD input side be canceled and directly connected to the input terminal? Will it have an impact on the sampling of the VS terminal and thus have a great impact on the output overvoltage feedback loop?
3.In addition to the UCC24612 synchronous rectification chip, are there other synchronous rectification chips for the UCC28780 control chip? (such as UCC24650)
4.Are there any selection requirements for the switch tube in the active filter circuit at the HVG end of the control chip UCC28780?

Thanks for the support!
  • 0
    TI__Expert 7080 points

    Hi Sirui,

    1. Could you please clarify what is "Active dual-position flyback", I am sorry that I never heard about it before. I guess it's active clamp forward , am I right ?

    2. VDD of UCC28780 can't be directly connected to the input voltage even it in the voltage spec. of VDD.  since auxiliary winding has much functions at different time slots, such as , sense input voltage / output voltage ,demarginating duration etc.  and if some faults happens , VDD will restart , so VDD caps will be discharged to VDD(OFF), If VDD connected to Vin , it can't be discharged.

    3. The best SR part for UCC28780 is UCC24612 in TI roadmap. UCC24650 is a wakeup chip rather than a SR controller.

    4. Do you mean the HV start up and VDS sense mosfet which connected to HVG and SWS pins . if so , depletion MOS is ok , just like BSS126.

    Thanks.

  • 0 in reply to Jaden Ning
    TI__Intellectual 2090 points

    Hi Jaden,

    Thanks for answering.

    Jaden Ning said:
    Active dual-position flyback

    You are right, it's 'active clamp flyback'. Is UCC28780 suitable for 70W 24V/24V isolated DCDC circuit if MOSFET Vgs(th)=4V?

    BR

    Sirui

  • 0 in reply to Sirui Zhu
    TI__Expert 7080 points

    Hi Sirui,

    UCC28780 can't support active clamp forward. 

    for 70W 24V/24V application , I still suggest you to chose Active clamp forward topology. the proposed device is UCC2897A.

    Thanks.