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UCC2894: Questions about soft-stop operation

Kaji@PAN
Mastermind 7215 points
Part Number: UCC2894
Other Parts Discussed in Thread: UCC2897, , UCC2897A

Hi,

I previously asked about UCC2894D in the following thread.
I would like to ask additional questions.
(question 1)
Is there any other documentation on the mechanism by which the primary switch overvoltages occur?
(Question 2)
In the answer to the previous question, it was stated that the appropriate soft stop time setting depends on the output capacitor and output voltage.
Specifically, is there a mathematical formula that quantitatively shows how the soft stop time is set at what voltage and how much capacitor capacity is?
(Question 3)
Is there any material that describes the difference between when the primary side main switch is overvoltage and when it is not?
(Question 4)
In the case of UCC2894D, is it okay to recognize that the soft stop continues to output both OUT and AUX, and the duty of OUT gradually decreases?
(Question 5)
I looked at the catalog of UCC2897.
The Line Undervoltage Protection section looks like the OUT pin is completely off.
In the UCC2894D catalog, it seems that DUTY is gradually changing for both OUT and AUX.
Is there any difference between UCC2897 and UCC2894 in the operation of soft-stop?

Best regards,

e2e.ti.com/.../962157

  • 0
    TI__Guru 53385 points

    Hi,

    Soft stop is the same for OUT to follow. AUX in UCC2897A is for P-Channel, and in UCC2894 for N-Channel. But that is the relation between AUX and OUT, the OUT following soft stop is the same.

  • 0 in reply to Hong Huang
    Mastermind 7215 points

    Thank you for your reply.
    I think your answer is the answer to questions 4 and 5.
    Is it possible for me to get 1-3 answers from you?
    Best regards,

  • 0 in reply to Kaji@PAN
    TI__Guru 53385 points

    (question 1)
    Is there any other documentation on the mechanism by which the primary switch overvoltages occur?

    [Hong Huang] LineOV pin set up the input voltage over voltage, there is no particular protection on the primary switch.


    (Question 2)
    In the answer to the previous question, it was stated that the appropriate soft stop time setting depends on the output capacitor and output voltage.
    Specifically, is there a mathematical formula that quantitatively shows how the soft stop time is set at what voltage and how much capacitor capacity is?

    [Hong Huang] The only formula is for the soft stop time shown in the datasheet. You need to find out how much time is needed to a particular design. 


    (Question 3)
    Is there any material that describes the difference between when the primary side main switch is overvoltage and when it is not?

    [Hong Huang] No, there is no particular protection for primary switch over-voltage. The input voltage over voltage is determined by LineOV.