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Original question:

TPS92515: Inquiry about an efficiency

TPS92515: Specifications and TPS92515 calculator

sho
Prodigy 40 points
Part Number: TPS92515

Hello teams,

I would like to ask you the following questions.

Q1.analog diming
 In the data-sheet, it is indicated that a lower limit is eventually reached when the measured peak threshold voltage is approximately < 50 mV.
Can I calculate a minimum current when a voltage applied on an Iadj pin is 50mV?

Q2.abusolute maximum rating
This data-sheet shown that the highest value of an abusolute maximum rating of the Iadj pin is 5.5V.
Does this mean that I can apply 5.5V on the Iadj pin without applying input voltage on a Vin pin?

Q3.Cin (TPS92515 Calculator Rev2 vs data-sheet)
This is the equation 21 in page 23 of the data-sheet.
I calculated a CIn-min by substituting ILED, fsw, toff, ΔVin-pp, but the answer was different from the result of calculating a CIn-min by the TPS Calculator Rev2.xls.
In this calculator, an equation in the column J of row 112 is "=………*2*2.5".
Please let me know the meaning of "*2" and "*2.5"?

Regards,

  • 0
    TI__Mastermind 28655 points
    Hello sho,

    1) When the TPS9515 gets to the minimum on-time the inductor will slew up to a level determined by V = L*(di/dt) and be off depending on Vled and the off-timer. This can be calculated but can vary quite a bit.

    2) "Does this mean that I can apply 5.5V on the Iadj pin without applying input voltage on a Vin pin?" That is not what that means. It means the abs max of the pin is 5.5V which I wouldn't apply since there is no margin however it turns out that 5.5V can be applied without Vin on this part. This is not true with all parts.

    3) they are for capacitor derating with applied voltage and for margin. If you look at a ceramic capacitor datasheet the capacitance rolls off with applied DC voltage. It can be minimal or rather large depending on the dielectric, value/voltage, and manufacturer. Otherwise the equation is I = C*(dv/dt) rearranged.

    Best Regards,