LT6000/LT6001/LT6002
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12
APPLICATIO S I FOR ATIO
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The input offset voltage changes depending on which
input stage is active; input offset voltage is trimmed on
both input stages, and is guaranteed to be 600µV max in
the PNP stage. By trimming the input offset voltage of
both input stages, the input offset voltage over the entire
common mode range (CMRR) is typically 400µV, main-
taining the precision characteristics of the amplifier.
The input stage of the LT6000/LT6001/LT6002 incorpo-
rates phase reversal protection to prevent wrong polarity
outputs from occurring when the inputs are driven up to
2V below the negative rail. 30k protective resistors are
included in the input leads so that current does not
become excessive when the inputs are forced below V
–
or
when a large differential signal is applied. Input current
should be limited to 10mA when the inputs are driven
above the positive rail.
Output
The output of the
LT6000/
LT6001/LT6002 can swing to
within 30mV of the positive rail with no load and within
30mV of the negative rail with no load. When monitoring
input voltages within 30mV of the positive rail or within
30mV of the negative rail, gain should be taken to keep
the output from clipping. The
LT6000/
LT6001/LT6002
can typically source 10mA on a single 5V supply, sourc-
ing current is reduced to 4mA on a single 1.8V supply as
noted in the electrical characteristics.
The normally reverse-biased substrate diode from the
output to V
–
will cause unlimited currents to flow when the
output is forced below V
–
. If the current is transient and
limited to 100mA, no damage will occur.
Start-Up and Output Saturation Characteristics
Micropower op amps are often not micropower during
start-up characteristics or during output saturation. This
can wreak havoc on limited current supplies, in the worst
case there may not be enough supply current available to
take the system up to nominal voltages. Also, when the
output saturates, the part may draw excessive current and
pull down the supplies, compromising rail-to-rail perfor-
mance. Figure 1 shows the start-up characteristics of the
LT6000/LT6001/LT6002 for three limiting cases. The cir-
cuits 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 circuit brings the
output up at 1/2 supply. In all cases, the supply current is
well controlled and is not excessive when the output is on
either rail.
SUPPLY VOLTAGE (V)
0
SUPPLY CURRENT PER AMPLIFIER (µA)
12
16
20
4
60012 F01
8
4
10
14
18
6
2
0
10.5
21.5
3 3.5 4.5
2.5
5
OUTPUT LOW
OUTPUT HIGH
OUTPUT AT V
S
/2
–
+
30mV
V
S
Output High
–
+
V
S
/2
V
S
60012 F02
Output at V
S
/2
–
+
30mV
V
S
Output Low
Figure 1. Start-Up Characteristics
Figure 2. Circuits for Start-Up Characteristics
