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UCC28730-Q1: HV startup

Ponkamali P
Prodigy 100 points
Part Number: UCC28730-Q1
Other Parts Discussed in Thread: UCC28730

Tool/software:

Hi,

One of the reference designs for UCC28730 shows HV pin pull resistance of 900k for 60V-1000V Vin. (Refer image)

According to datasheet, the start-up current required is 250uA typ.

The design referred here provides

60V/900k = 66uA.

Can you explain the selection of this HV start-up resistor?



Thanks

  • 0
    TI__Guru* 85446 points

    Hello,

     

    Your inquiry has been received and is under review.

     

    Regards,

  • 0 in reply to Mike O'
    TI__Guru* 85446 points

    Hello,

    It looks like they did not plan on a 60 V startup. You are correct that these resistor should have been smaller to support the 60 V startup requirement.

    Another option to drop the HV voltage would have been to use an NPN transistor as drawn below.

    Thank you for interest in Texas Instruments (TI) products.  If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

    Regards,