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UCC256403: some questions

anson zhou
Intellectual 335 points
Part Number: UCC256403

Tool/software:

Hi Sir :

I have the following questions regarding this chip ：

Question 1: Is there any way to determine the design margin of OCP2/OCP3 for this chip through testing or theoretical calculations?
Question 2: Will the soft start time of the chip end prematurely due to excessive feedback current from the FB pin?
Question 3: After the soft start time is over, will the driver be turned off first and wait for the configured hiccup mode threshold to end before releasing the driver? Is the configuration time around 7.5ms?;

Question 4: After mass production, some batches of machines have a soft start time of around 1.8ms, while others have a soft start time of around 35ms. After the soft start time of 1.8ms ends, OCP protection will be triggered. What is the reason for the difference in soft start time? How can we avoid this difference in the design process?

Question 5: As shown in the red circle in the figure below, the LL/SS pin of the actual machine did not charge to 5V before soft start as specified in the specification book. What is the reason for this? What impact will it have?

Question 6: After configuring the hiccup mode threshold, is BMTH fixed at 0.6V, while BMTL is determined by BW pin resistance?

  • 0
    TI__Genius 16155 points

    Hi Anson,

    Please see my responses below:

    anson zhou said:
    Question 1: Is there any way to determine the design margin of OCP2/OCP3 for this chip through testing or theoretical calculations?

    It can be done through testing. All you need to do is use the math function  and multiply the HO (make sure the signal is attenuated such that voltage level is 1 or 0)and ISNS signals and find the average of the math function

    anson zhou said:
    Question 2: Will the soft start time of the chip end prematurely due to excessive feedback current from the FB pin?

    Yes, if the FBreplica goes below soft start voltage, soft start phase will be ended.

    anson zhou said:
    Question 3: After the soft start time is over, will the driver be turned off first and wait for the configured hiccup mode threshold to end before releasing the driver? Is the configuration time around 7.5ms?;

    Driver wont be turned off. The burst mode thresholds will be programmed as explained below. 

    anson zhou said:
    Question 4: After mass production, some batches of machines have a soft start time of around 1.8ms, while others have a soft start time of around 35ms. After the soft start time of 1.8ms ends, OCP protection will be triggered. What is the reason for the difference in soft start time? How can we avoid this difference in the design process?

    Could you send me the LL/SS pin voltage when the soft start time is 1.8ms. Does the LL/SS pin reach 3.5V at the 1.8ms? Could you confirm?

    anson zhou said:
    Question 5: As shown in the red circle in the figure below, the LL/SS pin of the actual machine did not charge to 5V before soft start as specified in the specification book. What is the reason for this? What impact will it have?

    Could you attach the figure?  I am not sure which figure you are referring to?

    anson zhou said:
    Question 6: After configuring the hiccup mode threshold, is BMTH fixed at 0.6V, while BMTL is determined by BW pin resistance?

    While BMTH is fixed at 0.6V, BMTL is programmed to the threshold as set by the BW pin resistance. This determination of burst mode thresholds ratio happens before charge boot state as shown below. 

    Regards

    Manikanta P