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UCC2808-1: UCC2802 block diagram

MG74275
Intellectual 290 points
Part Number: UCC2808-1

I think there is an error in the block diagram. There are two comparators tied to the Softstart line. One has  threshold of VDD-1V but the softstart spec on pg 5 says the SS range is 0.5V to 4.0V.  What is the correct threshold?

  • 0
    TI__Mastermind 34465 points
    Hell MG74275,
    Sorry about your confusion with the block diagram. The line you refer to (labelled "soft start" in the block schematic) actually represents
    the power to the error amplifier of the PWM controller. The voltage on this line represents the instantaneous voltage during soft start and the max voltage available for the output of the error amp ( the COMP pin). When this voltage is below 0.5V , soft start is actively pulled low and PWM is disabled. Also if this voltage gets to within 1V of VDD then the soft start is pulled low and the system re starts. These are protective features for the soft start . Normal operation is for soft start at 0.5V and a final value of about 4V.
    Regards
    John