LT1677C View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LT1677C' PDF : 16 Pages View PDF
LT1677
APPLICATIO S I FOR ATIO
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
mode voltage approaches the positive rail (VCC – 0.7V),
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
resistors RC1, RC2 is reduced to less than 200mV, degrad-
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.
TYPICAL APPLICATIO
Microvolt Comparator with Hysteresis
INPUT
3+ 7
LT1677
2–
4
10M
5%
8
6
15V
365Ω
1%
15k
1%
OUTPUT
–15V
1677 TA02
POSITIVE FEEDBACK TO ONE OF THE NULLING TERMINALS
CREATES APPROXIMATELY 5µV OF HYSTERESIS. OUTPUT
CAN SINK 16mA
INPUT OFFSET VOLTAGE IS TYPICALLY CHANGED LESS THAN
5µV DUE TO THE FEEDBACK
12
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