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UCC28950: Difference between datasheet and application note

Hirotsugu Kobayashi
Mastermind 9790 points

Part Number: UCC28950
Other Parts Discussed in Thread: UCC28951,

Tool/software:

Hi team,

I have some questions.

1. Whereas the circuit in the data sheet is a voltage divider from CS The application note is a partial pressure from VREF. Which is correct?

2. The calculation of tABSET differs between equation (3) in the data sheet and equation (128) in the application note. Why are they different? I would like to know the derivation flow of each formula.
3. There is no derivation of RDELAB calculation from tABSET in the data sheet. This calculation method is only available in the application note, but I would like to know the main derivation method.
4. RTMIN has different derivation equations in data sheets and application notes. Which is correct? Also, I want to know the meaning of each number. 5.92/15ns/6.6s Also, I would like to know what should be used as a target for TMIN. Also, I would like to know what are the upper and lower limits.
5. Rsum differs in derivation calculations between data sheets and application notes. Why are they different? Also, I don't know the formula or concept of VSLOPE in the application note, so I would like to know it.
Best regards,
  • 0
    TI__Expert 3370 points

    Hi Hirotsugu San,


    Please allow me a day to respond on this.

    Regards
    Hemanth

  • 0 in reply to Hemanth Sreeperumbudur
    TI__Expert 3370 points

    Hi Hirotsugu San,

    Thanks for your patience.

    Due to Thanksgiving holiday, we are currently running with limited bandwidth. So, I couldn't get back to you with our response yet.

    Please allow me a day more to get back to you.

    Regards
    Hemanth

  • 0 in reply to Hemanth Sreeperumbudur
    TI__Expert 3370 points

    Hirotsugu-San,

    1. Both are correct. For adaptive delay, connect the ADEL, ADELEF dividers to CS pin; for fixed delays connect ADEL, ADELEF dividers between VREF and GND as explained in datasheet.

    2. tABSET expressed in terms of resonant frequency (equation 128 in app note) is to represent the maximum delay time to be set. This is an initial value as mentioned in the app note. tABSET in equation 3 of datasheet is actually used to calculate RAB from an initial value of tABSET .

    3. RDELAB is referred as RAB in datasheet. RAB can be calculated from equation 3 in datasheet, for a given  tABSET. You just need re-adjust the equation.

    4. As mentioned in the datasheet, after the equation (8), various propagation delays and response time delays in power circuit modify the actual pulse width.  The initial formula is mentioned int he datasheet. The adjusted empirical formula is mentioned in the application note. 

    As referred in datasheet - select RTMIN based on observed data and iteration process on a given board.

    5. RTMIN minimum and maximum values are as mentioned in the figure 6-7 in datasheet (10kohm to 140kohm). Accordingly the TMIN would be achieved.

    6. Connect RSUM to GND for Peak Current Mode Control (PCMC). Connect RSUM to VREF for voltage mode control (VMC). Equation (13) and equation (14) provides the RSUM values by reverse calculating for PCMC and VMC respectively.

    Please refer literature for understanding the requirement and amount of slope required for your application.

    It is a good idea to read the UCC28950 / UCC28951 datasheet in full as you design the converter using UCC28950 / UCC28951.

     

    Click on "Ask a new question" if you have more questions. Click on "Ask a related question", if you have any specific question related to the thread.

    Thanks for considering TI products.

    Regards

    Hemanth