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TPS22990: CT and Iinrush calculation

Kazuhiko Hirano
Genius 14028 points
Part Number: TPS22990

Hello,

 

I have following questions about CT and Iinrush calculation.

 

Q1:

Though datasheet Table 1 shows CT up to 10000pF, could CT be larger for example 0.1uF, 1uF or 10uF?

 

Q2:

Datasheet 10.2.2.1 shows how to calculate Iinrush when RL=None.

When RL is exist, for example 1ohms, how Iinrush could be calculated?

 

Best regards,

 

K.Hirano

  • 0
    TI__Mastermind 32650 points

    Hi Hirano-san,

    1. Yes. Even though the data is not spec in the datasheet, you can use CT capacitors higher than 10nF. 

    2. If in series, the cap charge time and inrush current will be determined by the final RC constant. The device will still turn on linearly with the turn on time specified by the CT cap. I think the best way of finding out the true inrush is to either use the EVM to test this or to use the PSPICE model on ti.com. Timing is very sensitive and so the calculations provided are only for the specified use case. In the case where the R_load is parallel to the cap, the inrush current seen by the cap should be the same while the total current through the device is inrush + current through R.