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TPS62130 Along with LM26480 Power supply failing

Purnenduk90
Prodigy 165 points
Other Parts Discussed in Thread: LM26480

I am designing a power supply for custom application that has FPGA along with many other ICs. Schematic and footprint is attached.

 

After working for a while, VCC_3.3V is following REG_EN pin, and power is drawn from REG_EN pin. So I removed the first stage and second stage seems to work in no load condition, but when loaded, gives half the output for 2.5 V, and more than 1.4V for 1.2V output.

Same thing happened to another board also, only it showed same behaviour after 2 day of operation. Where should I look at.

Inductor currents are already within limit.

  • 0
    TI__Guru**** 150870 points
    To debug any buck converter, you need to look at Vin, Vout, SW, and inductor current with a scope and see if they are as they should be. As well, you can measure the input current to your system and see if it is much higher than it should be--this would likely indicate one or both ICs are damaged.

    Depending on how you connect power at VCC_RAW, you may need more input capacitance to overcome the impedance of the input connection and prevent hit-plug overshoot as I explain here: e2e.ti.com/.../what-is-that-giant-tantalum-cap-on-the-input-of-the-evm
  • 0 in reply to Chris Glaser
    Prodigy 165 points

    one of the major problem I found that due to very small capacitance at soft start, there was an overshoot of current upto 2.5A, hence I have increased the SS/TR capacitance.

    What I want to ask that Inductor current is negative for small duration in LM26480, is it safe.

    Please see the simulation output of IL2 and IL3 they are output from LM26480 is any change required in this.

    sim4I.pdfsim4v.pdf