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LM3480 self destructs without load

Rafal Mroz
Prodigy 100 points
Other Parts Discussed in Thread: LM3480

Hello,

I'm using LM3480 to drop voltage from 24V down to 5V at very low current (<2mA). It's the standard application with 0.1uF for Cin and Cout. There is also a ferrite bead before the Cin and another ferrite bead after Cout. There is literally nothing loading the regulator (without regulator soldered in the resistance from Vout pin to both GND and positive rail is >1M. 

Despite all that the regulator seems to self destruct itself, It starts to draw gradually higher and higher current until self destruction. The thermal protection never kicks in. 

What might be the reason for such behaviour? Did I miss anything in the datasheet? Right now it looks like the regulator simply self destructs.

  • 0
    Prodigy 20 points

    I too am having a large percentage of failures of this regulator testing the units with no load.  Output capacitor is 10 uF, input is 4.7 uF in parallel with 0.1 uF.  Supply is 24 VDC.  Board is a mature product for over 8 years, never had this kind of issue.  Testing a sample lot of 50 pieces with a 20 volt input resulted in 0 failures, moving that up to 24 volts and retesting the same pieces resulted in 17 failures.  Output voltage typically goes to supply levels.  So devices appear to be sensitive to higher input voltages, even though spec says they can tolerate 30 volts.  I had some old National Semiconductor parts in lab to replace the blown ones with, they all worked just fine.  So what has changed in the last year?  We have tried a second lot of parts and this later lot was even worse on failure rates.  It appears something has changed in the manufacture of this device.