I have the following circuit:
Power filtering:
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:
There is nothing else on the board (unpopulated)
Layout:
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?
