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UCC28950 won't start.

Jim Walker61
Prodigy 50 points
Other Parts Discussed in Thread: UCC28950

I have a pdf of the relevant part of the schematic that I can send privately. The UCC28950 seems to be inhibited from starting but I have checked the more obvious inputs and they seem ok.  Supply voltage is 12V.  SS/EN is lifted - open circuit and reads 4+ V.  EA+ is at 4.5V while Vref is 5.04V.  CS is zero.  After having 12V applied for several minutes, there are some output pulses but I do not see any effect from them on CS or EA+

  • 0
    Prodigy 50 points
    I did solve that problem and if someone else has a similar situation, my observation is that the UCC28950 will not function with the internal error amplifier operating outside of its normal specified range (0.5V to 3.8V). The data sheet states that it is functional up to the ref voltage but it is not. My application required a ground reference and more precision than available with the internal amplifier so I used an external amplifier and then connected the internal amplifier as a buffer. I found it necessary to attenuate the signal from the external amplifier and I also added a resistor from COMP to EA-.
  • 0 in reply to Jim Walker61
    TI__Mastermind 31580 points
    Hi Jim,

    I will forward your findings onto our system engineer and ask hime to comment.

    Regards

    Peter
  • 0 in reply to Peter Meaney
    TI__Mastermind 25570 points
    Thanks Jim
    I was unaware of this behaviour. I'll try to verify this and maybe add a comment to the DS to the effect that the EA output may need to be clamped.
    Regards
    Colin