LM111/LM211/LM311
8.0 Application Hints
7.
(Continued)
When both inputs of the LM111 are connected to active
signals, or if a high-impedance signal is driving the
positive input of the LM111 so that positive feedback
would be disruptive, the circuit of
is ideal. The
positive feedback is to pin 5 (one of the offset adjust-
ment pins). It is sufficient to cause 1 to 2 mV hysteresis
and sharp transitions with input triangle waves from a
few Hz to hundreds of kHz. The positive-feedback signal
across the 82Ω resistor swings 240 mV below the posi-
tive supply. This signal is centered around the nominal
voltage at pin 5, so this feedback does not add to the
V
OS
of the comparator. As much as 8 mV of V
OS
can be
trimmed out, using the 5 kΩ pot and 3 kΩ resistor as
shown.
8. These application notes apply specifically to the LM111,
LM211, LM311, and LF111 families of comparators, and
are applicable to all high-speed comparators in general,
(with the exception that not all comparators have trim
pins).
00570429
Pin connections shown are for LM111H in the H08 hermetic package
FIGURE 1. Improved Positive Feedback
00570430
Pin connections shown are for LM111H in the H08 hermetic package
FIGURE 2. Conventional Positive Feedback
11
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