• Resolved

LM2904B: Offset Voltage is different from manual

Prodigy 40 points

Replies: 4

Views: 62

Part Number: LM2904B

I want to check LM2904B with TINA-TI simulation.

this parts spec is

- Input offset voltage : typ ±0.3mV

- Input bias current : ±10nA

- Input offset current : 0.5nA

in simulation, bias/offset current is right. but, input offset voltage is showing difference result. 

I don't know why the 6uV is different.

I guess, that circuit check to RTO. not sure..

  • Well Bruce, 

    The modelled input offset voltage is kind of a non-zero placeholder to make sure typ circuits show some output offset. That 6uV delta from typ is actually much closer than most models. Normally the typ specified Vos is 1 standard deviation of a 0 centered distribution. The models do not attempt to span the full spec range normally. 

    If that 6uV delta bothers you, add an external 6uV DC source, but that accuracy is a bit illusory given the full spec range at 25C of +/-3mV for the B version. 

    Michael Steffes

  • In reply to Michael Steffes:

    Then, can i understand that the above deviation is a limitation of simulation?

    I think, meet similar result values at a reasonable speed, 

    spice model parameters are limited and not be exactly configured.

    it was right?

  • In reply to bruce lee4:

    Hello Bruce,

    The limitation is more so with the models than with the simulation itself.  The simulation is capable of that precision, but the model has to balance several AC and DC specifications.

    The results for the model will reflect the typical values.  So your real world circuit(s) will not have the exact same results.  But, the model provides an accurate representation of a typical unit.

    Regards,
    Daniel

  • In reply to bruce lee4:

    Hello Bruce,

    Just wanted to add that I also agree with Michael's response.  The addition of 6uV of offset does not mean too much in the scale of the offset.  Consider that the offset will change from unit to unit in a much more significant way.  This is probably why the model designer did not try to match the offset to exactly 300uV and balance it with other part parameters.

    Regards,
    Daniel