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maximum hysteresis from a LM311?

I'm looking to use a LM311 to square up a signal from a opamp on +/-15V rails.

The configuration I'm using is to have positive feedback to the +pin via a

100k resistor and a 10K resistor from the plus pin to ground. Output is 0 - 3.3V (1k pullup) so that gives about 300mV of hysteresis. The signal is applied to the - pin.

I'd like to increase this to at least twice this level. I've been warned not to give too much positive feedback or it will oscillate. How much hysteresis have you guys gotten out of this part with this type of configuraion.

The designs in the app note have a high parts count and I'd like to keep it simple if possible.

Reply to
Mook Johnson
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So drop the 100k resistor to 47k.

Try to remember who warned you, and pay less attention to their advice in the future.

Hysteresis in comparators is usually used to kill oscillations, by forcing the comparator to switch rapidly between one stable configuration and another. Getting a comparator stable when you haven't got much hysteresis to keep the inputs away from the sensitive region requires you to be very careful with layout and power supply by- passing, to block the sorts of feedback paths that can support oscillation.

The standard triangular wave and sawtooth wave generators typically run with a hysteresis of about one third of the supply voltage. 600mV should be fine.

Changing the value of one resistor won't increase the parts count.

-- Bill Sloman, Nijmegen

Reply to
bill.sloman

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