• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 48 subscribers
  • Views 733 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM2901: Burn out when VCC not supplied, +ve input connects to capacitor and -ve input connects to 24 V

Lok Wei Hern
Prodigy 120 points
Part Number: LM2901

This part is not biasing/supplied by any power rails at all.

The +ve input (pin 7) is connected to the capacitor, while the -ve input (pin 6) is connected to 24 V across resistor.

The capacitor then get burnt out with smoke, followed by this part package body near +ve input get damaged too.

Removing the part from the board with observation that the +ve input pad is also get split off.

Wondering that is it too much current flow into -ve pin that breaks down the internal transistor (which isolates -ve & +ve pins?) and causing the current flows to +ve pins?

Thanks.  

  • 0
    Guru 140200 points
    Hi Lok,

    can you show a schematic?

    Kai
  • 0 in reply to Lok Wei Hern
    TI__Guru 55596 points
    Hello Lok,

    Has there been any developments on this?

    You should be able to bring the inputs up to 36V regardless of the supply voltage (even zero) without damage. However, if there is a negative glitch that brings any pin briefly below ground, this could trigger a destructive latch-up. The LM2901 family does NOT like negative input voltages.

    What is the voltage on VREF? How is the VREF voltage generated? Is it also at 0V?

    A capacitor "smoking" is very unusual. Is it a ceramic or Tantalum? What is the value? Does it blow right away? Or take a few seconds/minutes? Is the board supply current higher than expected?

    Tantalums can blow-up violently if the voltage is reversed - so check your polarity (is it in backwards?). They usually start getting warm first by drawing excessive current (10's-100's mA) when reversed - then blow when they have had enough. Same for Electrolytic, but with messier results.

    A ceramic (or other non-polarized) capacitor "smoking" would require a voltage applied greatly exceeding the working voltage, or a large high-frequency AC voltage applied.

    Have you watched the inputs and supply with a scope during turn-on/off? It sounds like there is a negative voltage on the VREF line - that is the only thing I can think of that would cause a tantalum capacitor to "smoke" and also severely damage the input.