12

LT1677

APPLICATIO S I FOR ATIO

Microvolt Comparator with Hysteresis

LT1677

3

7

1677 TA02

4

6

8

2

15V

–15V

OUTPUT

POSITIVE FEEDBACK TO ONE OF THE NULLING TERMINALS

CREATES APPROXIMATELY 5

µV OF HYSTERESIS. OUTPUT

CAN SINK 16mA

INPUT OFFSET VOLTAGE IS TYPICALLY CHANGED LESS THAN

5

µV DUE TO THE FEEDBACK

INPUT

10M

5%

365

Ω

1%

15k

1%

TYPICAL APPLICATIO

voltage noise of the op amp, i.e., the low voltage noise

specification is completely wasted. In this region the

LT1792 or LT1793 is the best choice.

Rail-to-Rail Input

The LT1677 has the lowest voltage noise, offset voltage

and highest gain when compared to any rail-to-rail op

amp. The input common mode range for the LT1677 can

exceed the supplies by at least 100mV. As the common

the tail current for the input pair (Q1, Q2) is reduced,

which prevents the input pair from saturating (refer to the

Simplified Schematic). The voltage drop across the load

ing the slew rate, bandwidth voltage noise, offset voltage

and input bias current (the cancellation is shut off).

When the input common mode range goes below 1.5V

above the negative rail, the NPN input pair (Q1, Q2) shuts

off and the PNP input pair (Q8, Q9) turns on. The offset

voltage, input bias current, voltage noise and bandwidth

are also degraded. The graph of Offset Voltage vs Com-

mon Mode Range shows where the knees occur by

displaying the change in offset voltage. The change-over

points are temperature dependent, see Common Mode

Range vs Temperature.