This question is regarding comparator with internal hysteresis.
Let a comparator having an internal Hysteresis "X"mv.
1. The spec table has min, typ and max values for a comparator with built-in hysteresis. Example is AD790.
2 and 3. The external hysteresis set by the user will overwrite the internal hysteresis. Please refer to page 4 of this document.
Thank you very much.
Could you please check the below link,it says external hysteresis will get added to internal hysteresis.
First let me correct my term from "overwrite" to override". Sorry for the confusion.
In the TI forum link you posted, it discusses about the hysteresis transfer function when there is a built-in hysteresis which is Vos (offset voltage) +/- Vhys/2 (Vhys here pertains to the built-in internal hysteresis only). This was also presented in the page of 3 of the MT-083 document from ADI I sent you with additional illustrations. Though the answer in the TI forum mentioned that "external hysteresis will get added to internal hysteresis", there is no subsequent example or back-up to support the statement.
Now going back to your question and the question in the TI forum that you mentioned, will the internal and external hysteresis add up? The answer based on the document I sent you is that the external hysteresis that you will set using positive feedback with resistors will override or dominate the hysteresis. There is an article in Maxim which showed how to dictate the hysteresis or hysteresis band externally with resistors and how to compute its values when the comparator has built-in hysteresis. If I'm not mistaken the comparator in the example has 4mV built-in hysteresis but it was extended to 50mV using the external resistors in positive feedback.
Hope this helps.
I got the MAXIM Application note.
I have one more question
" In a dual opamp if I use one opamp as amplifier and other as a comparator will it cause any stability issues."
Some of the main causes of instability in opamp is the input/output capacitance loading. There are other factors as well as discussed in this app note.
Using one opamp as amplifier and other channel as comparator will unlikely cause instability.