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LM319 open collector comparator - what is the minimal voltage supply for the output resistor ?

LTest.1
Associate

‎2020-09-24 11:41 PM

I'm using the LM319 open collector comparator with a 12V power supply. What is the minimal voltage supply for the output resistor load ? I need a 1.8V logic output so I would like to power the output resistor with a 1.8V voltage.

Is there a minimal voltage for the output resistor ?

Thanks a lot.

Luca.

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Peter BENSCH
ST Employee

‎2020-09-25 05:47 AM

The LM319 was designed many, many years ago, when low voltage logic was not yet known.

You should also consider the input requirements of the following logic inputs, as well as the size of the pull-up resistor. With an open collector output, you should carefully check the case when the output tries to drive low level. You can find information regarding this in the datasheet, e.g. at fig 4: output saturation voltage, which in the worst-case will be about 0.27V when the current through the pull-up is at 1mA. If the 270mV is correctly recognized as low by the following logic input you could e.g. use a pull-up of 1500 ohms and connect it to the 1.8V logic voltage.

Good luck!

/Peter

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