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LM2904: The application problems of LM2904

Shaw Wong
Intellectual 590 points
Part Number: LM2904

Hi,

Our customers use LM2904 to control fan, the schematic as follows. But they found some chip are abnormal: the voltage of pin 1 and pin 2 are 11.3V( normal voltage are 1.5-5V ).

And we tested these abnormal chip, found that the impedance between pin1(1OUT) and pin8(VCC) is very low(about 22 ohm). So we judged these chip are broken down during operation.

Now we want to know what reason may cause breakdown of channel 1? And can you give us some suggestions of design? Thanks!

  • 0
    TI__Guru**** 156916 points
    Shaw,

    I don't see any problem in schematic that would cause damage. The motor could have large transient voltages, but the two resistors and capacitor should be sufficient to prevent damage.

    How often does this happen (failure rate)? When does this happen (production field)? Is the a new or old design?
    Could they provide a waveform for "IN_FAN_FB-" when running and during fan turn on and off.
  • 0 in reply to Ron Michallick
    TI__Guru**** 156916 points
    Shaw,

    I am marking this thread as resolved for metrics. You may post again to reopen the thread or mark as not resolved.
  • 0 in reply to Ron Michallick
    Intellectual 590 points
    Hi Ronald,

    Thanks for your answer. Our customer does not give us some feedback so far. I will tell you whenever customer gives any feedback, thank you!