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TPS92515HV: Design Caculator

Ryuji
Guru 20090 points
Part Number: TPS92515HV
Other Parts Discussed in Thread: TPS92515

Hello,

I have 2 questions about TPS92515 design calculator.

(1) Cin_min
In the design calculator, the Cin-Min is multiplied by 5 (2*2.5)  at the end of the calculation by excel calculation formula.
Why is this?
I could't found the information of this "5" in the datasheet.

In the datasheet calculation is CIN-MIN=ILED*(1/fsw - toff) / ΔVin-pp only. Not multiplied by 5.


(2) Vout Shunted
There is the Vout shunted cell for R7 Value for shunted condition.
The Vout shunted value is 0.5V in the calculator and I couldn't change this value.

Should we use 0.5V for Vout shunted? 
If yes, please let me know this reason.

Best Regards,
Ryuji

  • 0
    TI__Mastermind 25500 points

    Hello Ryuji,

    I spoke to the person that developed the tool. To answer your questions:

    1. He multiplied by 2.5 to make sure it meets the minimum capacitance requirements even after you account for capacitor tolerances, the temperature range, and the capacitance drop due to bias voltage. He multiplied by another 2 just for extra margin. In reality the more you have the better in general and if you are doing any form of PWM dimming I would personally multiply the value the tool gives you 2 or 3 times again at least.

    2. This is an oversight on his part, he locked that cell on accident. You can unprotect the sheet using the password "TPS92515" (no quotation marks) and enter your own value. Vshunt should be the shunt FET Rds(on) times the output current.

    Regards,

    Clint

  • 0 in reply to Clinton Jensen
    Guru 20090 points
    Hello Clint,

    Thank you for your reply.
    I have additional question about design calculator.

    Why are hidden lines 30 to 33 on the excel sheet?
    Parameters that need confirmation such as ILpkpk and toff are hidden.

    Best Regards,
    Ryuji
  • 0 in reply to Ryuji
    TI__Mastermind 25500 points

    Hello Ryuji,

    The calculator developer said it was just to simplify things and make sure somebody didn't accidentally replace an equation with a manual input. You can just unhide them, but be careful not to accidentally overwrite and equation.

    Regards,

    Clint