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LMP7708: Abnormal waveform output

Kelley Kim
Prodigy 70 points
Part Number: LMP7708

Dear,

I purchased below part through MOUSER on 1/26 and I found a failure issue.

LMP7708MAX/NOPB /  16ea 
Although I purchased through Mouser, they can't help on this directly due to their internal system.
So, Mouser advise me I need TI confirmation that it's a technical defective for the exchange the items. 
Please see below defective symptoms.
 
- A waveform is formed just by flowing current as a single item. 
 When entering current for buffer (noise removal), the same waveform should come out, but it didn't.
1st pic : a waveform inputting 1.2V 
2nd pit : a waveform inputting 2V

Please check whether it's technical issue or not, then I'll ask for an exchange to Mouser.
Thank you.
  • 0
    Guru 140200 points

    Hi Kelly,

    can you show a schematic?

    Have you noticed that the LMP7708 is a decompensated OPAmp and needs a minimum gain of factor ten?

    Kai

  • 0
    TI__Guru 63050 points

    It does sound like you use LMP7708 in a buffer configuration but as Kai said in order to be stable this op amp requires higher close-loop gain.

    In order to stabilized decompensated op amps, you must increase the close-loop gain, Gmin, so it crosses AOL at f2 or lower frequency. In case of LMP7708 recommended min gain is 10 or higher - see below.