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I am inspecting the LM339 datasheet (link) and I find contradictory information regarding the operation principle.
Page 10 states:

The output consists of an open-drain NPN (pulldown or low-side) transistor. The output NPN sinks current when the positive input voltage is higher than the negative input voltage and the offset voltage.

But page 12 says:

If IN– is higher than IN+ and the offset voltage, the output is low and the output transistor is sinking current.

Which one should be considered?

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    \$\begingroup\$ Errk. An NPN BJT with a drain? Don't those have collectors? \$\endgroup\$
    – JRE
    Commented Nov 3, 2018 at 13:29
  • \$\begingroup\$ FYI this datasheet contradiction has been mentioned before, in this answer to a different question. \$\endgroup\$
    – SamGibson ♦
    Commented Nov 3, 2018 at 15:02

2 Answers 2

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The text on page 10 is incorrect, that is clear when you look at the schematic: enter image description here

The output NPN sinks current when the positive input voltage is higher than the negative input voltage and the offset voltage.

No, when the IN+ has a higher voltage, more current will flow through the right side of the differential pair (the side connected to IN-), and pull the voltage at the NPN current mirror up, that will switch on the NPN that has the 80uA source connected to its collector and then means that the output transistor will be off. So that NPN cannot sink current at all.

Amazing that there are still errors like that in a TI datasheet. And talking about a drain, hmm. Someone wasn't paying attention.

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Since it's a comparator, we know if - is greater than +, the output will be low. The text on page 12 is correct.

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    \$\begingroup\$ I agree, the text on page 10 is incorrect, that is clear when you look at the schematic. When the positive input voltage is higher than the negative input voltage the output transistor is switched off. Amazing that there are still errors like that in a TI datasheet. And talking about a drain, hmm. Someone wasn't paying attention. \$\endgroup\$
    – Bimpelrekkie
    Commented Nov 3, 2018 at 14:46
  • \$\begingroup\$ @Bimpelrekkie The work of some intern? The part has been around for probably > 40 years (it's not shown as new in my 1982 NS Databook). \$\endgroup\$
    – Spehro 'speff' Pefhany
    Commented Nov 3, 2018 at 16:22
  • \$\begingroup\$ Thanks @Bimpelrekkie, can you please formalize your comment as an answer with the schematic explanation so it can be selected as the accepted answer? Thanks \$\endgroup\$
    – jagjordi
    Commented Nov 3, 2018 at 16:25
  • \$\begingroup\$ @jagjordi it is done. \$\endgroup\$
    – Bimpelrekkie
    Commented Nov 3, 2018 at 16:48

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