• State TI Thinks Resolved
  • +1 person also asked this people also asked this
  • Locked Locked
  • Replies 5 replies
  • Answers 3 answers
  • Subscribers 35 subscribers
  • Views 560 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

UCC25660: How to disable HV startup

Conor
Guru 12540 points
Part Number: UCC25660


Tool/software:

Hi,

Q1. The datasheet describes "HV startup" on pages 33 and 55. What process is required to disable HV startup on UCC256601?

Q2. Please tell me how to calculate FBreplica listed on the TSET pin.

Specifically, I would appreciate it if you could teach me the details of how to derive the formula for FBreplica enclosed in the red frame. The document states that this relationship can be derived from RISNS, CISNS, CR, RBLKupper, and RBLKlower.

Q3.
Is it correct to understand that to disable burst mode, the VLLA-VLLB voltage should be set to the range of 2.185 to 2.41V?

Thanks,

Conor

  • 0
    TI__Guru 50190 points

    Hi Conor,

    For question #1 - If HV startup is not required, you can simply tie the HV pin to GND. 

    For question #2 - FBreplica can be measured from the current out of the FB pin. To calculate FBreplica the datasheet shows the following:

    Where IRFBinternal= 80μA and RFBinternal ~100kΩ 

    What you need to do is subtract the current measured out of the FB pin from IRFBinternal. So

    FBReplica= RBFinternal*(IRFBInternal- IFB(measured))

    For question #3 - Yes. Tset above 2.185V will diable burst mode. 

    I hope this answers your questions.

  • 0 in reply to JCHK
    Guru 12540 points

    Hi JCHK,

    JCHK said:
    For question #2

    I understand that Fbreplica can be calculated in the section 7.3.3 Feedback Chain.

    However, the datasheet states that Equation 60 (FBReplica = 0.0076Pin + 1.7364) can be derived from Equation 4 (FBReplica = 2/Cr*K1* Pinavg + K2*Iramp). I would appreciate it if you could tell me the process of deriving the relationship between Equation 60 and Equation 4.

    Thanks,

    Conor

  • 0 in reply to Conor
    TI__Genius 16155 points

    Hi Conor,

    At this point of time, we cannot give you the derivation of that equation. However, you should be able to use the design calculator to see the relation between the FBReplica and Input Power. 

    Regards

    Manikanta P

  • 0 in reply to Manikanta Pallantla
    Guru 12540 points

    Hi Manikanta,

    Thank you for your reply.

    Manikanta Pallantla said:
    At this point of time, we cannot give you the derivation of that equation. However, you should be able to use the design calculator to see the relation between the FBReplica and Input Power. 

    I looked at the design calculator below, but I couldn't find any description showing the relationship between FBReplica and Input Power.

    You wrote, "we cannot give you the derivation of that equation." Why? The data sheet says that it can be derived, so I would like to know how to derive it.

    Thanks,

    Conor

  • 0 in reply to Conor
    TI__Genius 16155 points

    Hi Conor,

    There is a graph that shows VFBReplica vs Power in the same sheet of the design calculator as shown below.

    The primary reason for not showing the derivation is that some of the patents related to the contents are currently pending. To ensure the integrity and confidentiality of the intellectual property involved, I believe it is prudent not to show the internal implementation.

    Regards

    Manikanta P