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UCC2897A: About the setting of UCC2897A

Kaji@PAN
Mastermind 7815 points
Part Number: UCC2897A


Hi,

I would like to ask you about the UCC2897A device.
(question 1)
If I don't use the overvoltage protection function (LINEOV), can I set the LINEOV pin to GND?
(Question 2)
The data sheet shows the maximum duty under certain conditions (see figure below), but what is the maximum duty for this device in practice?
Under the conditions of RON = 87kΩ, ROFF = 54kΩ, and RDEL = 10kΩ, I have confirmed that the board I made can output up to about 77% ON Duty.
(Question 3)
The data sheet states that the external sync frequency should be set higher than the free-running frequency.
Is the following setting possible?
external sync frequency x 0.9 > free-running frequency

Best regards,

  • 0
    TI__Guru 74115 points

    Hi,

    (question 1)
    If I don't use the overvoltage protection function (LINEOV), can I set the LINEOV pin to GND?

    Yes, you can.


    (Question 2)
    The data sheet shows the maximum duty under certain conditions (see figure below), but what is the maximum duty for this device in practice?
    Under the conditions of RON = 87kΩ, ROFF = 54kΩ, and RDEL = 10kΩ, I have confirmed that the board I made can output up to about 77% ON Duty.

    The maximum duty cycle is related to the switching frequency selected, then minus the dead-time, and rise and fall time. So a lower switching frequency can have a bigger maximum duty. Equation 5 in the datasheet shows maximum duty cycle calculation.


    (Question 3)
    The data sheet states that the external sync frequency should be set higher than the free-running frequency. Is the following setting possible?
    external sync frequency x 0.9 > free-running frequency

    It means you want to set up external sync > 1.11 free-running frequency. Yes that is ok. But you should be aware of the free-running frequency has a tolerance, about 10%. So your external sync should be > 1.11 x (1.1) free-running frequency, or, ext sync freq > 1.23 free-running frequency.