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LMV981-N: Seems the gain charts do not match specified gain-bandwidth product

Remi Demers
Prodigy 20 points
Part Number: LMV981-N

I have the datasheet revision M. The GBW is specified as 1.4 MHz but all the gain charts seems around a 10-fold lower. In Figures 6, 7, 8 and 9, no one show a zero dB gain over 1Mhz. It is more ranging from 400 kHz to 800 kHz. Since the datasheet have reached rev. M., I guess there is something I do not understand to explain this apparent discrepancy. Please explain! Thank you!

  • 0
    TI__Guru*** 142726 points
    Remi,

    The data sheet tables (that say 1.4MHz) live under the table defaults which include load 1 Mohms.
    The bode plots in typical char graphs use a 600 ohm load and show a GBWP of 800 kHz
    The reduction is 800 kHz/1.4 MHz = 57%
    Load is 600 ohms. The output impedance that would give 57% is 600 ohms * 43%/57% = 452 ohms
    Because data is not from same device, I would NOT fully trust that typical Out-Z is 452 ohms.
    This does show why there is a difference between data sheet table and typical charts.
  • 0 in reply to Ron Michallick
    Prodigy 20 points
    Hey thank you Ron, this makes a lot of sense to me. Around the same topic, I was trying to guess an equivalent output resistance, and you gave me the trick. I did not notice the RL=1M in the table top, that was the key. Thanks again.