Datasheet
8
LT1672/LT1673/LT1674
Start-Up Characteristics
Micropower op amps are sometimes not micropower
during start-up, wreaking havoc on low current supplies.
In the worst case, there may not be enough supply current
available to take the system up to nominal voltages. Figure
1 is a graph of LT1673 supply current vs supply voltage
for the three limit cases of input offset that could occur
during start-up. The circuits are shown in Figure 2. One
circuit creates a positive offset, forcing the output to come
up saturated high. Another circuit creates a negative
offset, forcing the output to come up saturated low, while
the last brings up the output at half supply. In all cases, the
supply current is well behaved. Supply current is highest
with the output forced high, so if one amplifier is unused,
it is best to force the output low or at half supply.
APPLICATIO S I FOR ATIO
WUUU
TOTAL SUPPLY VOLTAGE (V)
0
SUPPLY CURRENT PER AMPLIFIER (µA)
5
4
3
2
1
0
4
1672/3/4 FO1
1
2
3
5
OUTPUT V
S
/2
OUTPUT HIGH
OUTPUT LOW
Figure 1. Start-Up Characteristics
16/2/3/4 F02
OUTPUT HIGH
V
+
V
–
V
–
V
–
V
+
V
+
–
+
OUTPUT AT V
S
/2
–
+
OUTPUT LOW
–
+
820k
200k
Figure 2. Circuits for Start-Up Characteristics
Reverse Battery
The LT1672/LT1673/LT1674 are protected against reverse
battery voltages up to 18V. In the event a reverse battery
condition occurs, the supply current is typically less than
100nA (inputs grounded and outputs open). For typical
single supply applications with ground referred loads and
feedback networks, no other precautions are required. If
the reverse battery condition results in a negative voltage
at either the input pins or output pin, the current into the
pin should be limited by an external resistor to less than
10mA.
Inputs
While the LT1672/LT1673/LT1674 will function normally
with its inputs taken above the positive supply, the com-
mon mode range does not extend beyond approximately
300mV below the negative supply at room temperature.
Small-Signal Response Small-Signal Response Large-Signal Response
TYPICAL PERFORMANCE CHARACTERISTICS
U
W
V
S
= ±15V
C
L
= 100pF
A
V
= 5
V
S
= 5V
C
L
= 100pF
A
V
= 5
V
S
= 5V
C
L
= 100pF
A
V
= 5
1672/3/4 G19 1672/3/4 G20 1672/3/4 G21