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TPS62173/TPS62172 - TPS62173 doesn't work, TPS62172 does.

Robert Sifuentes
Prodigy 20 points
Other Parts Discussed in Thread: TPS62173, TPS62172

Designed board using both for 3.3/5V. Am using same components for both circuits. TPS62172 outputs 3.3 Volts as advertised, TPS62173 outputs 5.8Volts on one board and 5.9-6.3 (depending on load) on the other. Loads for both are <400 mA. Attached file shows schematic, layout and scope displays. TPB62172-3.pdf

  • 0
    TI__Guru*** 142860 points
    Thank you very much for your well documented problem.

    Your layout looks decent, but you should rotate the input cap on both ICs 180 degrees so that they bypass the Vin and PGND pins. As well, I would recommend making your Vin line to both ICs thicker. It has to carry some current too. You might try this on a board and see if it helps.

    Your third scope capture shows that the IC is not switching. This sometimes means that a voltage is being applied on the output by something else. Based on your 7.4V input voltage, this could be coming from the input somewhere. i.e. through a silicon diode installed backwards for example. You can remove L4 from the board and see if the 6V is still there.
  • 0 in reply to Chris Glaser
    Prodigy 20 points

    Chris,

    You are brilliant. D7 was installed reversed. Pulled it out and works just fine. I was thinking the 6 Volts was coming out of the chip. Thanks for that and the layout tips.

    Robert Sifuentes