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What is the benefit with comparators that have a Hysteresis pin?

What is the benefit with comparators that have a Hysteresis pin?

I'm using one the LTC1440 and I don't see any benefit you still require two resistors for Hysteresis. Is the Hysteresis pin tied internally to the output (positive feedback)?

If I wanted to use this comparator in an inverting mode can I still use the suggested method in the application note for Hysteresis (pg.11)? Or should I use the standard method a resistive divider off the output back to the reference?

LTC1440 Datasheet (Hysteresis is on pg.11)

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Hysteresis for inverting comparator

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Thanks

Reply to
Hammy
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External hysteresis, like in your second link, has lots of problems. Fast noisy inputs can blow through the comparator, and make multiple output edges, before the positive feedback arrives. Comparators with internal hysteresis usually do it right.

It's amazing how often the 2-resistor external thing is used and documented, even though it's inherently flawed.

John

Reply to
John Larkin

Thanks for the reply John :

I'm still a bit confused (surprise ;).

Are you saying that the sole porpose the Hyst pin is there to save on propagation time? The LTC1440 response time is measured in uS so would this still be beneficial at these speeds?

Reply to
Hammy

This pin can only apply up to 100mV +/- 15% of Hysteresis. Its faster in the since that its only swinging 100mV around. Most of the time I will measure the Hysteresis to see just how much is really needed. This is completely dependent upon the noise at the input to the comparator.

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