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LM2903B: Delay is 1000us instead of 300us in simulation.

Derek Belsky
Prodigy 45 points
Part Number: LM2903B


I am looking for a comparator that has a switching time under 1us and I found the LM2903B which had the following specification which satisfies this. 


So, I tried to simulate the LM2903B in PSPICE with similar test conditions but I am getting a 1000ns switching time which matches with the second specification and not the first. I have included an image of my simulated circuit and its output.

Any thoughts on why I am not seeing the 300ns switching time. Thank you. 

Derek Belsky

  • +1
    TI__Guru 61996 points

    Hello Derek,

    Simple. The model uses a worst case number. The model does not take into account the overdrive factors.

    The 300ns is with a large input signal - which is huge for a comparator. The 1us is for a 5mV overdrive (overdrive is the amount of signal over the threshold).

    Please see the propagation delay graphs on page 16. These will show you what you should expect as far as speed.

    Do not try to "push" the device as fast as it can go...speed can vary over process ±15% or more...so if you need speed, it is better to get a faster comparator rather than try to push a slower one to it's limits.