I'm building a simple circuit which has an LM211 comparator at its heart. The positive input is connected to a 10k-10k resistor divider across the supplies, stabilized by a 1uF capacitor. Hysteresis is provided by 1.8MOhm from the output to the positive input.
The signal on the SENS line is a slowly changing resistance hooked up to +5V on the other side.
Everything works perfectly on a breadboard, but I wanted to check a few things before finalizing the board layout, and came across a TI application note which says in paragraph 6:
It is a standard procedure to use hysteresis (positive feedback) around a comparator, to prevent oscillation, and to avoid excessive noise on the output because the comparator is a good amplifier for its own noise. In the circuit of Figure 2, the feedback from the output to the positive input will cause about 3 mV of hysteresis. However, if the value of Rs is larger than 100Ω, such as 50 kΩ, it would not be reasonable to simply increase the value of the positive feedback resistor above 510 kΩ.
However, it doesn't say why a high value feedback resistor is "not reasonable". I built up my circuit on a breadboard, and it seems to work fine, I can definitely see good hysteresis behaviour with the 1M8 resistor as compared to without it.
So, what is the drawback?