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UCC2894: What is the UCC2894's action when shut down signal on SS/SD terminal from external signal soruce

user5817567
Prodigy 20 points
Part Number: UCC2894
Other Parts Discussed in Thread: UCC2891

I wolud like to konw UCC2894's action (functional sequence, timing, some conditions etc) when shut down signal on SS/SD terminal from external signal soruce.

Please inform me any technical document.

/ Condition

  The UCC2894 was operating normal before shut down signal input.  

  The shut down signal is low which holding long time (ex: 1sec low ). 

  • 0
    TI__Mastermind 34465 points

    Hello ,

    There are no special timing diagrams for the SS/SD pin except what is described in the data sheet.

    A capacitor (CSS) connected between this pin and GND (pin 6) programs the soft start time of the power converter. The soft-start capacitor is charged by a precise, internal DC current source which is programmed by the RON resistor connected to pin 2. The soft-start current is defined as:

    ISS = 0.43 * RTON = 0.43 ( VREF/2 )* (1 /RON)

    This DC current charges CSS from 0 V to approximately 5 V.
    Internal to the UCC2891 family of controllers, the soft start capacitor voltage is buffered and ORed with the control voltage present at the FB pin (pin 9).
    The lower of the two voltages manipulates the controller’s PWM engine through the voltage divider described with regards to the FB pin.
    Accordingly, the useful control range on the SS pin is similar to the control range of the FB pin and it is between 1.25 V and 4.5 V approximately.

    Regards

    John

  • 0 in reply to John Griffin1
    Prodigy 20 points

    Thank you. I resolved.