LM27761: wrong output and device overheating

Lizi Xiong

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

over 7 years ago

0 Chris Glaser over 7 years ago

TI__Guru*** 148870 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 Chris Glaser over 7 years ago in reply to Chris Glaser

TI__Guru*** 148870 points

Hi Lizi,

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

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LM27761: wrong output and device overheating