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TPS6040x input capacitor needed?

Scott Miller1
Intellectual 515 points
Other Parts Discussed in Thread: TPS60400, LM2664

I am going to possibly use TPS60400 in a design to provide the negative rail to an op amp for a bipolar output.  My design is very space sensitive, and I would like to know if the input capacitor is needed if I am feeding the device with a switching power supply. with 10uF and 0.1uF in parallel on the output of the switching power supply.  The TPS60400 will be very close to the switching power supply.  I plan to use 1uF fly and output caps on the TPS.

  • 0
    TI__Guru**** 150880 points

    Yes, all 4 caps are required.  Being a switching power supply, the TPS6040x requires capacitors to store and transfer the energy.

    A 1 uF cap comes in an 0201 package, so hopefully you have this much room on your board for one.  Or you could change the 0.1uF on the output to a 1uF and move it to the input of the charge pump.

  • 0 in reply to Chris Glaser
    Intellectual 515 points

    Your LM2664 does not require the input cap, which is why I was hoping the TPS6040x did not require it either.  But I imagine that the internals are somewhat different.  And I'm guessing that one is a NI design or BB and the other is a TI design.

    I do my own prototypes, and because of that I tend to use 0402 as the smallest size resistor.  Ceramic capacitor makers don't tend to post their ESR numbers, so I was shying away from using any capacitor series that is not specified on your datasheet.  The TPS device does not specify a max ESR like the LM device does. If using any ceramic capacitor is ok, then I will use 0402 caps and probably be ok on board space.