LM2901: LM2901

Hi Roi,

what do we see in the scope plot? What are the input signals?

Also, rethink the handling of unused inputs of comparators:

snoaa35b.pdf

Kai

The yellow signal in the scope plot is the LM2901 output, the green signal is output of my next component that his input connected to the LM2901 output (not that relevant, this is the picture I have).

IN- pin connected to reference voltage of 1.2V, and IN+ pin connected to testing voltage, in steady state is lower than 1.2V, so the output of the LM2901 is 0V.

Hi Roi,

this can be ground noise. If you have a microcontroller in your circuit this noise can come from the 3.3V supply or can be common mode noise on the signal ground. Best remedy is to use a solid ground plane and to route the analog and digital ground strictly separated from each other.

I would take such a ground spring and connect it directly to the ground pin of LM2901:

Are you still seeing this noise at the output of LM2901?

Can you show your layout?

Another cause could be sporadic togglings or even oscillations in your LM2901 itself due to the mishandling of unused inputs of comparators. This could cause some unwanted ground bounce within the LM2901.

Also keep in mind that the maximum input voltage of LM2901 is 3.3V - 2V = 1.3V.

Kai

Hi Roi,

How is the reference voltage generated?

And as Kai mentioned, the legal input range of the LM2901 comparator is Vcc-2, or 1.3V on a 3.3V. So make sure both inputs are below 1.3V.

Is it possible to see both inputs, output and supply voltage all on one scope shot? So that we can see the actual action of just the comparator and the actual I/O conditions.

Would this "next level" circuit cause any transients or supply droop when it activates?