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TPS62140 Input Capacitor less than 10uF?

Sagar Dastidar
Prodigy 60 points

Datasheet recommends a 10uF for Cin.  Are there any stability issues with reducing the size of this cap to 1uF?  My application has an in-rush current limitation where a 10uF capacitor's peak current is not going to work.

 

Thanks

 

  • 0
    TI__Guru**** 150900 points
    Being a SMPS, enough input capacitance is required to provide the cycle by cycle charge for each switching cycle. I would not recommend going below 10uF Cin.

    Can you share details of your application? What is Vin? What is limiting the inrush current? A resistor or current limited switch between the input supply and input cap is a possible option.
  • 0 in reply to Chris Glaser
    Prodigy 60 points

    Vin is +15V.  The source of Vin is another subsystem with a rise time of roughly 120 microseconds.  So, the 10uF cap is coming out to 1.25A.  (C* dv/dt).  I like the resistor option  - I am assuming we are talking about a series resistor to limit the current?

     

    Thanks

  • 0 in reply to Sagar Dastidar
    TI__Guru**** 150900 points
    Yes, a series resistor is one option. Anytime you add impedance on Vin, you will likely need to add more C after it to overcome it.

    I would also recommend checking in our power interface forum. Those guys may have an eFuse or other current limiting IC which would work out better. If not, you could build one discretely with an RC on the gate of a PFET for example to delay the application of Vin to the 10uF.