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# LM393B: Difference in VOL and max stable input voltage of LM393B and LM393

Part Number: LM393B
Other Parts Discussed in Thread: LM393, , LM393LV

Hi Team,

Our customer would like to know some details about the operation on the newer LM393B compared to the older LM393 specifically if there are any differences in VOL (the small output voltage that depends on the pull up resistor/current). He also wants to know if we have a general equation for calculating VOL @ 25C for the lm393 and the lm393b.

Lastly, if he is using a 5.4 VCC supply and the max input level to the comparator is 3.7V, he would like to know if this is stable. According to him, he read somewhere that input voltage between 3.5V to 4.0V range can be unstable.

Regards,

Danilo

• Hi Danilo,

have you seen figure 6-25 of datasheet? Keep in mind that the typical performance is shown in this figure but no guaranteed limits. These you will find in the table from section 6.7 of datasheet. Look for the VOL and IOL specifications. Also, what output current are we talking about?

The common mode input voltage range is up to 1.5V below supply voltage at room temperature. Moving away from room temperature the common mode input voltage range is only up to 2.0V below supply voltage. Taking your numbers

5.4V - 2.0V = 3.4V

would be the allowed common mode input voltage range when moving away from room temperature. So 3.7V input voltage would definitely be outside this "green" range and could make issues.

Kai

• Danilo

Kai has provided a good response.  One follow up comment in regard to the recommended common mode range is related to the voltage on each individual input.  Specifically, is the customer interested in having the voltage on each pin go as high as 3.7V?  Or is only one pin going as high as 3.7V.  The LM393B and original LM393 family has a unique input stage that allows one pin to go outside the range if the other input is within the range.

Lastly, if the VCC voltage is only up to 5.4V, it may be good to consider our new 5V version of the LM393 which we call LM393LV.  This device does not have the common mode limitation of the 36V LM393 comparators.  It is a CMOS device featuring a rail to rail input stage.  So if the supply voltage is max of 5.4V, then this may be a good option to consider.  Pinout and package options are the same.

Chuck