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I have the following circuit:

Power filtering:

enter image description here

The 330 μH chip inductor has about 10 Ω series resistance. I scoped the powerup to 5 V and the overshoot even with no load was minimal (maybe 300 mV).

Oscillator circuit:

enter image description here

There is nothing else on the board (unpopulated)

Layout:

enter image description here

My problem:

The LMV7239 instantly burns and clamps the supply DVDD to 1 diode drop above DGND.

I was initially supplying a regulated 5 V to VIN from a lab power supply.

I removed the LMV and checked all nodes and they bias correctly as you would expect if U7 is not populated. In particular, I could measure the full DVDD, so there is no other path to DGND.

I re-placed a new U7 and slowly increased the supply voltage at VIN, starting from 0V. Everything looked alright until about 0.8V. Then, again the chip died clamping DVDD to ~0.7 V.

I removed the LMV again. And placed a 27 Ω resistor in series with VIN to be absolutely sure that there are no sub-µs voltage spikes from the bench power supply. I also scoped the supply and I couldnt see anything unusual apart from the 10s of mV of switching noise. I tried to power up the circuit again and the LMV died again instantly.

I also tried to attach the power supply to an unsoldered LMV7239 chip with tips, but it also died. However, it is possible that I slipped from the positive supply (2) to the IN+ pin (3) or the output pin (1). Still wouldn't expect it to burn due to this.

I have used this bench power supply for tests in the past and never faced problems.

My question:

Is there anything obviously wrong I am missing?

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1 Answer 1

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Based on your layout and text description, the pinout does not match the datasheet.

The positive and negative supply pins are swapped.

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    \$\begingroup\$ geez. I suppose that is obvious enough m-( It's what you get for sloppy last minute circuit changes due to BOM changes. I blame the chip crisis :-p \$\endgroup\$
    – tobalt
    Commented Dec 14, 2021 at 14:49
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    \$\begingroup\$ Just wanted to thank you again, because this same error had also seeped into other circuits, that are still under developement! \$\endgroup\$
    – tobalt
    Commented Dec 17, 2021 at 9:37
  • \$\begingroup\$ @Justme, I'm pretty impressed about how quickly you caught this... well-done sir! \$\endgroup\$
    – Abdella
    Commented Oct 23, 2023 at 8:58

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