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LM27761: wrong output and device overheating

Lizi Xiong
Prodigy 10 points
Part Number: LM27761

Hello. I am having problems with LM26671 regulator. I have input 5V, and want to generate -2V output with current draw of about 1mA.

I have the schematic and layout here.

What I am seeing is, after powering out, I would have output at -2V for some time, and then the output would go to 30 mV (VFB 10-20mV), and I can feel from the bottom of the board, the component is overheating.

What is the problem here?

Thanks very much.

I am attaching 

  • 0
    TI__Guru*** 148810 points
    Hi Lizi,

    Thanks for sharing your schematic and layout.

    I cannot see how the IC GND vias connect to the other GND vias. Do you have an internal GND plane on another layer or is this a 2 layer PCB? In any case, with any switching regulator we need a short and direct connection between the caps and the IC. You could order the EVM, with its known good layout, and see if it works for you.
  • 0 in reply to Chris Glaser
    TI__Guru*** 148810 points
    Hi Lizi,

    Can you share how the GND vias connect to each other?