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TPSM84624: Value of Rtt

user6004480
Intellectual 630 points
Part Number: TPSM84624

Tool/software:

Hi Expert,

Which should We adopt for Rtt, the value displayed on WEBNECH or the value calculated using Equation 3 in D/S?

For example
When We initiate WEBENCH with the settings VOUT=3.3V, VIN=5V+/-5%, IOUT=3A Ta=40, the value of Rtt is displayed as 4.32k by default.
On the other hand, when we substitute VOUT=3.3V, COUT=100uF, KTT=1.8(same as WEBENCH) into Equation 3, As a result of the calculation, the value of Rtt is 9.88k.
It seems that the value of Rtt is different.

  • 0
    TI__Mastermind 25330 points

    Hello,

    This is because the effective output cap is used in the equation - this is the cap as a result of using the DC bias characteristic from the manufacturers. The WEBENCH effective output cap is 48uF. Also, for 3.3V, KT=2. Using these values, the RTT value of 4.32k is correct and recommended. If you are using different caps, check with manufacturer DC bias characteristic data and use that value in this eqn.

    Thanks,

    Amod

  • +1 in reply to Amod Vaze
    Intellectual 630 points

    Hi Amod,

    Thank you for reply !