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UCC28950EVM-442 Controller

MG74275
Intellectual 290 points
Other Parts Discussed in Thread: UCC28950

1) The RT pin is tied to VREF (61.9kohm) which configures the part as a master but the SS/EE pin has a 825kohm resistor to GND for a slave configuration.  What does this combination master/slave accomplish vs. removing the 825kohm resistor?

2) Equations 10 and 11 in the Rev C datasheet compute Fsw vs. RT for master and slave configuration then has a comment that the equations are equal when VREF=5V.  The reference is fixed so when would these be different?

  • 0
    TI__Mastermind 25570 points
    The UCC28950 should operate correctly in slave mode if the 825k resistor is not fitted at the SS pin. The function of the 825k resistor is to prevent the SS pin exceeding about 5V. If the SS pin exceeds 5V then the SYNC function will not work although the slave device should run correctly at the frequency set by the resistor from RT to GND.

    Equations 10 and 11 calculate RT for the master and slave configurations. We include a note that VREF is 5V just as a reminder to the reader and you are correct that VREF will never be a different value. For a given frequency, RT will be the same in both master and slave configurations.

    Regards
    Colin