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UCC28704EVM-724: UCC28704EVM-724 modify for 36VDC Input

Cao Cao
Intellectual 770 points
Part Number: UCC28704EVM-724
Other Parts Discussed in Thread: UCC28704

Hi Team,

I plane use UCC28704 application PSE power. since UCC28704 has frequency dithering reduces the EMI peak energy.

Input range need cover 36VDC - 96VDC.

May I know UCC28704 is suitable use this application? if yes, please provide reference schematic for me, thanks.

  • 0
    TI__Expert 7395 points
    Cao Cao,

    Thanks for your interest in TI here. This part should potentially work. You need at least 23v on Vdd to start and shouldn't operate it above 35v on Vdd. Can you clamp the Vdd with a Zener or will that be a problem?

    What is the output voltage and maximum output current?

    Is this a POE application?

    Regards
    John
  • 0 in reply to John Stevens
    Intellectual 770 points

    Hi John,

    Yes. This application for PD extender. (.at 30W PD via extender deliver .af 15W PD)
    Extender basic diagram is PSE controller, so input spec is 36VDC - 58VDC(Maximum up to 96VDC ) and Output spec 12V/1.2A.

    1. We simulate by WEBENCH has VIN minimum condition.

    2. Looks UCC28704 schematic has start up current. I can set RSTR = 36V / 1.5u =  1M ohm ?

    3. Brown in / Brown out can effect out design?


    Cao Cao

  • 0 in reply to Cao Cao
    TI__Expert 5900 points

    Hi Cao,

    UCC28704 should work in your application.

    Regarding to the RSTR, you need to consider below two points.

    1. the charing current thru RSTR at (VDD on threshold) should be >2.5uA; (Vinmin-VVDD(on))/RSTR > 2.5uA

    2. The startup delay time should be reasonable. you may don't like wating 10s for the module to startup. the startup delay time is determined by the charging current on VDD, the VDD cap and the VDD on threshold. you could refer equation 10 in the UCC28704 datasheet

    Regarding Brown in/out function, from a preliminary calculation, if you set 30V as the typical brown in voltage, the range considering the tolerance of VSL(run) should be 26V-36V. and the Brown out voltage range should be 9.5V-13.5V. You should evaluate the effect based on your requirements and calculation. 

    Br

    Kening