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Original question:

UCC28063: The system does not start without load

UCC28063: UCC28063 Replace UCC28061 The system fails to start

Gabriel Wang1
Genius 3825 points
Part Number: UCC28063
Other Parts Discussed in Thread: UCC28061

Dear Expert

Ctm change UCC28063 to UCC28061 ,and system fails to start .The Pin5 COMP is low lever ,other pin voltage are normal.

Below is schemetic ,pls check!24v8a.pdf

  • 0
    TI__Genius 10555 points

    Hi, in order to help you, I need more information.  The schematic you provided is using the UCC28061 controller.

    1. Did the customer have a working solution with the UCC28061 and then change out the controller for a UCC28063?

    2. If the answer to 1. is YES, what other circuit changes did the customer make to accommodate the differences between the -061 and 063 controllers?  Please provide a schematic.

    3. If the answer to 1. is NO, can you please explain the situation more clearly and with more details.

    Thank you,

    Ray

  • 0 in reply to Ray DiCecco
    Genius 3825 points

    Dear Ray

    No circuit change ,ctm just use 063 replace 061 .

  • +1 in reply to Gabriel Wang1
    TI__Genius 10555 points

    Hi Gabriel,

    The UCC28063 is NOT a simple drop-in replacement for the UCC28061.  The customer should consult the two datasheets to understand what is different between the two controllers and change their application accordingly. 

    Although many of the improvements made to the -063 will not require changes to the application circuit, some likely will.  I've highlighted those features below:

    COMP:

    • 2-level EA gain, no slew-rate correction current
      • lower 50uS gM allows lower compensation component values
      • higher 250uS gM replaces slew-rate correction for fast response

             >COMP drive capability is lower, so attached circuitry must not overload it

    • Internal 2kΩ pull-down latched on COMP during BO, HVSEN_OV, UVLO with a 20mV full-soft-start-enable threshold

     

                 > Need to make sure Flyback PFC mods do not interfere with COMP being able to reach <20mV

    VINAC:

    • Lower VINAC hysteresis current
    • Dropout detection
      • 35V threshold, 5.3ms delay before action, 0.71V immediate clear
      • Suspend COMP voltage, add 4uA pull down current

    VSENSE:

    • Lower VSENSE hysteresis current