LMV321: Can LMV321 be used to a comparator ?

Hi Aggil,

there are several issues:

1. Why not using a comparator?

2. Why using so many diodes? Wouldn't be one diode enough?

3. You violate the common mode input voltage range of LMV321. See section 7.6 of datasheet. I would connect a resistor from pin 3 of LMV321 to GND forming a voltage divider to make the input voltage fall into the allowed common mode voltage range. Put a small capacitance in parallel to this resistor to filter out fast switching transients. The same for pin 1 LMV321. Don't connect +5V directly to pin 1 but use a suited voltage divider.

4. Having both inputs of LMV321 at 0V and observing 5V at the output of LMV321 does not necessarily mean that the LMV321 is damaged. Don't forget the effect of input offset voltage of LMV321.

5. Directly discharging C808 by Q28 can destroy the transistor. Insert a small current limting resistor.

Kai

Aggil,

Kai comments are valid.

When LMV321 has both inputs above the common mode range and the op amp is in open loop configuration, the output will be either near 0V or 5V. The input stage is cutoff so the next internal stage will have a zero difference input . This stage is not completely balanced, so most devices will go low but some will go high. If this stage was balanced then the low / high spilt would be 50/50.

LMV321A will not have this issue. The op amp will still see the input (no cutoff) even at input near positive supply rail. Therefore you must have an input voltage difference to get the desired output.

Because you care only about shorts where 12V falls below roughly 5V, no op amp is needed at all. A transistor could do the job.

Hi Ronald
Do you suggest a comparator to replace LMV321 ? It is better if they are P2P.

Hi 

  thanks, we will evaluate it.