LMP7708: Abnormal waveform output

Kelley Kim

Prodigy 60 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.

over 2 years ago

0 kai klaas69 over 2 years ago

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 Marek Lis over 2 years ago

TI__Guru 62300 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.

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LMP7708: Abnormal waveform output