LM2903B: Problems simulating the LM2903B

Martin Holguin

Part Number: LM2903B
Other Parts Discussed in Thread: LM339

Hello,

I am using the SPICE model indicated on their website at the following link . After adding it to LTspice, the simulation seems to work fine, but some strange pulses appear almost in the middle of the triangular test signal I use for my simulation. The first image is the circuit I am simulating, and the second one is the response I obtain. Is it possible that the SPICE model needs to be modified, or am I the one who is doing the simulation incorrectly?

5 months ago

+1 Paul Grohe 5 months ago

TI__Guru 67986 points

Hello Martin,

Your sim is correct, but your circuit is violating the input voltage range.

The LM2903B model has a feature where if the input voltage range is violated, the output is forced to 1/2 supply.

The LM2903B input range is up to VCC-2V. Notice that the output sets to 2.5V when the triangle passes 3V.

The model is working fine - it alerted you to a problem as intended.

For more info, see the LM339 family application note, sections 6.4 and 10 :

Application Design Guidelines for LM339, LM393, TL331 Family Comparators

If you do need the full input range, consider the LM393LV which is R-R input and would not have this issue.

0 Martin Holguin 5 months ago in reply to Paul Grohe

Intellectual 400 points

Hi Paul,

The answer you gave me was exactly what was happening. Thank you very much. I have already modified the part number of this device to avoid this issue.

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LM2903B: Problems simulating the LM2903B