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LM2904: LM2904DGKR output abnormal issue

Benjamin Zhou
Expert 4000 points
Part Number: LM2904


Hi Team,

  My customer is using LM2904DGKR, during the assemble line FCT test, 1PCs LM2904DGKR reported output abnormal issue;

  Have done the cross test, issue followed LM2904DGKR.  if powered up with +5V power supply, IN- short to OUT,  while input the 1Khz@3V Sine signal,  the normal and abnormal device shown the same result,  but while connect 20Kohm resister to IN- and OUT,  the normal device and abnormal device shown quite different waveform,  also the I-V curve of abnormal device has difference with normal device.

  Update the customer schematic and test waveform as attached file,

LM2904 issue.docx

  Need your kindly support for below items:

  1) schematic design;

  2) I-V curve;

 

Expect for your reply, thanks.

Best Regards

Benjamin

  • 0
    TI__Guru**** 165526 points

    Benjamin,

    For the 20k load test, I assume this load was terminated to ground. Does the device work if the load was terminated to VCC?

    1) The schematic seems to be fine.

    2) The IV curve is illegible, I could not read it.

    I can't tell for certian, but the LM2904 appears to be damaged. 

     

  • 0 in reply to Ron Michallick
    TI__Expert 4000 points

    Hi Ron,

      The 20Kohm resister is just connect to IN- and OUT pin,  and the OUT PIN is floating during the third test item. and on board test, the abnormal LM2904 output pin is connect to another LM2904 IN+ via resister and capacitor;

      What's the mean of terminated to VCC, connect the output PIN to VCC?

    Best Regards

    Benjamin

  • 0 in reply to Benjamin Zhou
    TI__Guru**** 165526 points

    Benjamin,

    From left to right, R1 is connected to out and in- the other end is floating (not terminated). R2 is connected to out and in- and R2 is terminated (the other resistor end) to ground. R3 is terminated at VCC.

    I suspect the problem device was damaged and my best guess is ESD (electrostatic discharge) damage. 

    I also tested a control device and here is the VOUT vs. VIN result for all three setups listed above.

  • 0 in reply to Ron Michallick
    TI__Expert 4000 points
    Ron,
    Very appreciated for your suggest, now is working with customer for the 3 typical schematic tests and next steps.
    Thanks very much.

    Best Regards
    Benjamin