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TPS54331 Power issue

sachin.munot
Prodigy 70 points
Other Parts Discussed in Thread: TPS54331

Hi,

I am using TPS54331 for power supply and it is giving output of 3.5V/3A.

As i am connecting this to my other power supply which is made of TPS75801 to generate 3.3V.

But my issue is when i connect both the power supply they give exact voltages.But for current requirements when surges comes in my load , one of my pcb stands good and provides 3A surge to TPS75801.But rest of PCBs don't. So can any body suggest me what are the things i could have missed?

The circuit design and components are both same in all the cases.

 

Regards.

  • 0
    TI__Guru**** 191445 points

    I'll need to see your schematic and any wave forms you can provide.  From what I understand your load is on the output of the TPS75801.  When you apply a 3 A load step, what happens on the good board and on the bad board?  Does the 3.3 V drop?  Does the 3.5 V drop? please provide a more detailed description along with schematics and wave forms.  After iget a good idea of your issue, I will ask for additional detailed waveforms.

  • 0 in reply to JohnTucker
    Prodigy 70 points

    Hi,

    As i tried some experiments i come to know following things.

    As TPS75801 is just a regulator it will need 3A at the input side when it has to provide the load 3A.Now in my case the good one PCB works fine because it can provide this current but in bad PCB the TPS54331 is not capable to provide the current.

    So the voltage level of TPS75801 goes down.What i have done is i have same designs for my TPS54331 in both good and bad PCBs. But for some reason one is cable of providing higher current and other is not.

    So i just want to know what could be the reasons i should check.

    And i have same designs which are given in TPS54331's datasheet.

     

    Regards.

  • 0 in reply to sachin.munot
    TI__Guru**** 191445 points

    You should start by monitoring the output current of the TPS54331 circuit.  The best way is to lift the output side of the inductor and connect it back the PCB using a short loop of wire.  Use a clamp on current probe to measure the current.  Look to make sure the peak current is not exceeding the OCP.  I have heard instances where inrush current of the linear regulator is high enough to cause problems.  check also the output voltage a SS voltage.  Look for any differences between the good and bad circuits.  Post your wave forms and I'll look for subtle problems.  Also, the circuit in the datasheet is designed for 3.3 V output, not 3.5 V.  You should be able to change the resistor divider to get  3.5 V out.  The circuit should still work properly at 3.5 V output, but it may be possible some other components need changing.  Pay close attention to the input capacitor location as well.  As close as possible...you cannot get it too close.