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LM321: LM321LVIDCKR issue

HH1992
Prodigy 120 points
Part Number: LM321
Other Parts Discussed in Thread: TLV9001

Tool/software:

Hi,

I’m using the LM321 as a voltage follower to read the main bus voltage, which ranges from 40V to 55V.

The issue arises when I increase the main voltage beyond ~52V. At this point, the output saturates at 3.3V and doesn’t change any more.

For example, at 52V, the input voltage (after the divider) is 2.73V, and if I increase it further to 2.8V, the output remains stuck at 3.3V.

I was wondering if there’s something I might be missing or misunderstanding.

Thanks!

  • 0
    TI__Guru* 77541 points

    Hi Gholam,

    HH1992 said:
    For example, at 52V, the input voltage (after the divider) is 2.73V, and if I increase it further to 2.8V, the output remains stuck at 3.3V.

    The simulation is a linear behavior model. When the input Vcm of an op amp is violated, the Spice model is unable to compute. So it will stuck in a default value. I think that this is what is going on. Tina and other simulator may behave slightly different, when an op amp is operating in non-linear range.  In addition, LM321 Spice model is old. 

    Best,

    Raymond

  • 0
    Guru 318700 points

    To allow input voltages up to 3.3 V, use an opamp with rail-to-rail inputs like the TLV9001‍IDCKR.