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UCC28740: HV Recommended Range Consult

Stanley Dai
Expert 5810 points
Part Number: UCC28740
Other Parts Discussed in Thread: PMP20432, PMP20396, PMP40376, TL431, UCC28730, UCC28711, UCC24650

Hi Team,

The HV start-up range in customer system is required between 40~600V. I didn't find the recommended range of UCC28740's HV pin in our D/S. Could you pls comment on here? Thanks.

Best,

Stanley

  • +1
    TI__Guru 50190 points

    Hi Stanley,

    When the HV pin charges VDD above its UVLO (~21V), The controller will start switching. 

    I hope this answers your question.

    Regards,

  • +1
    TI__Intellectual 1265 points

    Hi Stanley,

    Your customer should be able to start-up the UCC28740 at 40V, although many test result files from our reference designs like PMP20432, PMP20396, and PMP40376 show the UCC28740 starting up from ~100V DC. What's important to understand is their startup timing requirements, naturally a lower startup voltage will take more time to charge VDD capacitor up to 21V UVLo turn-on threshold.

    If the customer requires full output power/current at the lower input voltage, they'll have to make special considerations to carefully design the transformer and size the startup network to provide the required startup and Ivsl(run) level currents for the controller optimally over the full input range.

    I hope this helps. 

    Regards,

    Andrew

  • 0 in reply to Andrew Plummer
    TI__Expert 5810 points

    Hi Andrew,

    Do you know whether UCC28740 can support PSR or removing TL431+Opto-coupler here? Customer wants to save system cost because they don't need isolation here. It will be nice if you have design example here. Thanks.

    Best,

    Stanley 

  • +1 in reply to Stanley Dai
    TI__Intellectual 1265 points

    Hi Stanley,

    It is possible for some of our SSR controllers to support PSR. To my knowledge we do not have a reference design published on TI.com today that demonstrates this capability. Unfortunately within our team we do not even have a preliminary schematic or block diagram for the UCC28740.

    If they want to remove optocoupler solution based on cost reduction, why don't they use a PSR controller like the UCC28730? If they need fast transient response they could consider adding the UCC24650 wake-up monitor IC which could still save drastically on output capacitance. If not, try positioning the UCC28711, another PSR flyback controller where the final design would resemble the UCC28740 most closely, assuming the output capacitance is adjusted to improve transient response.

    Hope this helps...

    Regards,

    Andrew