LM111H datasheet(11/23 Pages) NSC

11 / 23 page

8.0 Application Hints (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 Figure 1 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 82

Ω 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

OS of the comparator. As much as 8 mV of VOS can be

trimmed out, using the 5 k

Ω pot and 3 kΩ resistor as

shown.

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

LM111H Datasheet(PDF) 11 Page - National Semiconductor (TI)