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TPS62152: No output voltage

Maarten Roozendaal
Prodigy 30 points
Part Number: TPS62152
Goodday,
I am currently working on a design that uses the TPS62152 DC/DC converter to convert 15VDC to a fixed 3.3VDC.
In the design process, I have paid close attention to datasheet suggestions regarding layout and surrounding components.
However, I have a problem: When I apply 15VDC to the input of the converter, I get 0VDC output (no output). 
At this moment the converter (whithout a load but with all surrounding components in the schematic) pulls arround 36uA.
I have tried replacing nearly all components except for the input filter but have had no success. I have made measurements
to make sure all surrounding components do in fact make contact with the IC and that everything is connected as should be.
At this point I am starting to think the problem is with a PCB manufacturing malfuntion and I am going to assemble a new pcb.
Can you confirm that the design is correct? I have included the schematics and the pcb design.
The IC is configured for 1.25MHz operation
I know this is a very broad question so let me know if I can supply any more details or made calculations.
Greetings,
Maarten
  • 0
    Prodigy 30 points
    Okay, so now I have assembled a second PCB which works fine. Outputs a stable 3.3V.
    Still, I have no idea why the same circuit will not work on the above PCB.
    I have replaced all components twice and it will just not work.

    For clarity: the above schematic and PCB design do work fine.
  • 0 in reply to Maarten Roozendaal
    TI__Guru*** 142880 points
    Hi Maarten,

    Thanks for this additional information. Yes, it sounds like something on the first assembly does not work right.

    Your schematic and layout look ok.

    Your next step is to look at the various signals with a scope on the first board and see what doesn't look right.
  • 0 in reply to Chris Glaser
    Prodigy 30 points
    Hi Chris,

    Thank for the response, I have looked at all the possible input/output pins available on the IC with a scope. I seems the converter will just not start switching and remains in shutdown, drawing only 20uA. The EN pin and SS/TR pin are also connected fine.

    Everything is soldered properly and all connections are fine.

    I do not know what the problem is, but now that I know that the design is okay I will just throw the problem board away.
    I guess these things just happen from time to time.

    Thank you.
  • 0 in reply to Maarten Roozendaal
    TI__Guru*** 142880 points
    Hi Maarten,

    Thanks for looking at the various pins. If you could share/post the waveforms or explain what voltage everything was at, we can try to isolate the problem.