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LM5160A: Sporadically blow up of IC; Short circuit

Christian Eckl
Prodigy 10 points
Part Number: LM5160A
Other Parts Discussed in Thread: LM5160

Tool/software:

Hi,

I'm using the LM5160A module in a functional test board. Sporadically I'm struggling with defects on the IC. Local overheating always occurs at the same position in the chip. I cannot explain why this happens.

What I can measure:

LM5160A shows DIE burnout. There is an internal short between VIN - SW - PGND. The short is also measured from VIN to TP (thermal pad). The LM5160A works well for a long time. The temperature is also within range. But sometimes it happens that the IC gets a short. We tried short-circuiting the 12V output for a long time (24 h) -> no problem for the design. Also shorting the input voltage, which leads to excessive current in the body diode of the high side mosfet, does not damage the IC. The temperature under full load conditions looks well.

Now I'm at the point where I can't get any more insight into the IC.

Who can help me? Thanks!

  • 0
    TI__Mastermind 39960 points

    Hello Christian,

    Any clues on when the device fails?  on start up?  during load step?  Can you share full schematic including input stage with any filtering you may have?

    Thanks,

    David.

  • 0 in reply to David Baba
    Prodigy 10 points

    Hi David,

    Thanks for your reply.

    The fault occurs when operating at ~ 0.6A output current with no load step. Shorting the output will not damage the IC.

    But we assume that the input voltage is not stable in some cases. So we have added the diode D? to the LM5160 schematic/board.

  • 0 in reply to Christian Eckl
    TI__Mastermind 39960 points

    Hello Chrisitan,

    Are you saying the failure occurs when the output is shorted?  If so, what do you mean the input voltage is not stable, does the input voltage have enough current capability to sustain a short on the output of the LM5160?

    My real concern is regarding the inductor, I believe its a ferrite and worse case current limit of this device is typically at the ISAT rating.  worse case it cannot sustain worse case peak currents without collapsing in inductance.    

    David.

  • 0 in reply to David Baba
    Prodigy 10 points

    Hi David,

    Thanks for your reply and help.

    The design is stable during an output short. A short will not damage the IC over time. The input power is up to 500W at a voltage level of 48V. But to be clear. During my evaluation some voltage drops down to 0V occurred. During this interruption phase of the power supply, the IC was - sometimes - damaged. This was the reason for adding an external diode to the design (marked D?) to discharge the output not via the internal body diode. But this didn't help much. In some cases the IC blows up, which we don't understand.

    Regarding the coil/inductor. Yes, that would be a potential failure mode. The nominal value given is 82 µH. The -20% inductance is at 2.8A. The -40% inductance is at 3.5A. The resulting inductance should be sufficient for this 1A step down converter. The calculated peak current is 1.7 A at full output load (1 A). The switching frequency is 270 kHz.

    Could you imaging an other failure mode?

    Christian

  • 0 in reply to Christian Eckl
    TI__Mastermind 39960 points

    Hello Chistian,

    If VIN drops to 0V and you have VCC connected you are in trouble, the device will get damaged.

    suggest disconnecting 12V VCC supply and retesting.  Thanks.

    David.