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UCC28631: Startup time

Linh Dang74
Prodigy 60 points
Part Number: UCC28631


On the datasheet page 15 the worst case startup time is 1.002s can this startup be lower?

I am connecting to a 180VDC source. 

  • 0
    TI__Mastermind 40580 points
    Hello Linh,

    The 1.002-s worst-case start-up time on page 15 is based on using a 22-uF VDD capacitor and 200kohm resistor to the AC line set at 90Vac. This time is for the specific circuit example described on that page, which includes X-cap discharge configuration.
    Start-up time can be significantly faster under different circumstances, provided the conditions are right.
    If you use a 180Vdc source with no other changes, equation 1 indicates that start up could be less than half that time.

    If you use the DC-connection as shown in Figure 15b (page 14) you can reduce or eliminate the series resistance Rhv to get higher start-up charging current. And you can investigate your circuit needs to see if Cvdd can be reduced from 22uF. All these options help to reduce start-up time.

    Regards,
    Ulrich
  • 0 in reply to Ulrich Goerke
    Prodigy 40 points
    Thanks for the answer. One other concern I have is compensation. Page 24 "The UCC2863x devices uses a novel
    internal compensation scheme to adjust for this parasitic voltage drop, and can deliver excellent static line and
    load regulation, even when operating heavily in CCM." So there is no need for external compensation network for this device?
  • 0 in reply to Linh
    TI__Mastermind 40580 points
    Hello Linh,

    That is correct. The internal compensation discussed to on page 24 of the UCC2863x datasheet refers to adjusting the sensed voltage to accommodate the effects of the output diode's declining voltage drop during the demagnetization interval. This requires no additional external network by the user.

    More generally, I think your question relates to voltage-loop compensation, and this too is automatically performed within the IC, as discussed on page 30 of the datasheet. No external loop-compensation network is required by the IC.

    Regards,
    Ulrich