Datasheet
12
LT1677
1677fa
APPLICATIO S I FOR ATIO
WUUU
General
The LT1677 series devices may be inserted directly into
OP-07, OP-27, OP-37 and sockets with or without removal
of external compensation or nulling components. In addi-
tion, the LT1677 may be fitted to 741 sockets with the
removal or modification of external nulling components.
Rail-to-Rail Operation
To take full advantage of an input range that can exceed
the supply, the LT1677 is designed to eliminate phase
reversal. Referring to the photographs shown in Figure 1,
the LT1677 is operating in the follower mode (A
V
= +1) at
a single 3V supply. The output of the LT1677 clips cleanly
and recovers with no phase reversal. This has the benefit
of preventing lock-up in servo systems and minimizing
distortion components.
Offset Voltage Adjustment
The input offset voltage of the LT1677 and its drift with
temperature are permanently trimmed at wafer
testing to a low level. However, if further adjustment of
V
OS
is necessary, the use of a 10kΩ nulling potentiometer
will not degrade drift with temperature. Trimming to a
value other than zero creates a drift of (V
OS
/300)µV/°C,
e.g., if V
OS
is adjusted to 300µV, the change in drift will be
1µV/°C (Figure 2).
Input = – 0.5V to 3.5V LT1677 Output
3V
2V
1V
0V
– 0.5V
1577 F01a
3V
2V
1V
0V
– 0.5V
1577 F01b
Figure 1. Voltage Follower with Input Exceeding the Supply Voltage (V
S
= 3V)
The adjustment range with a 10kΩ pot is approximately
±2.5mV. If less adjustment range is needed, the sensitiv-
ity and resolution of the nulling can be improved by using
a smaller pot in conjunction with fixed resistors. The
example has an approximate null range of ±200µV
(Figure 3).
Figure 3. Improved Sensitivity Adjustment
Figure 2. Standard Adjustment
1677 F02
10k
OUTPUT
INPUT
8
7
6
4
1
2
3
15V
–15V
–
+
LT1677
1677 F03
1k
4.7k
OUTPUT
8
7
6
4
1
2
3
15V
–15V
–
+
LT1677
4.7k
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