9
LT1077
1077fa
The LT1077 is fully specified with V
+
= 5V, V
–
= 0V,
V
CM
= 0.1V. This set of operating conditions appears to be
the most representative for battery powered micropower
circuits. Offset voltage is internally trimmed to a minimum
value at these supply voltages. When 9V or 3V batteries,
or ±2.5V dual supplies are used, bias and offset current
changes will be minimal. Offset voltage changes will be
just a few microvolts as given by the PSRR and CMRR
specifications. For example, if PSRR = 114dB ( = 2µV/V),
at 9V the offset voltage change will be 8µV. Similarly,
V
S
±2.5V, V
CM
= 0 is equivalent to a common mode voltage
change of 2.4V or a V
OS
change of 7µV if
CMRR = 110dB (3µV/V).
A full set of specifications is also provided at ±15V supply
voltages for comparison with other devices and for
completeness.
The LT1077 is pin compatible to, and directly replaces,
such precision op amps as the OP-07, OP-77, AD7O7 and
LT1001 with 30 to 60 times savings in supply current. The
LT1077 is also a direct plug-in replacement for LT1012
and OP-97 devices with 10 times lower dissipation.
Compatibility includes externally nulling the offset
voltage, as all of the devices above are trimmed with
a potentiometer between Pins 1 and 8 and the wiper
tied to V
+
.
The LT1077 replaces and upgrades such micropower op
amps as the OP-20, LM4250, and OP-90, provided that the
external nulling circuitry (and set resistor in the case of the
LM4250) are removed. Since the offset voltage of the
LT1077 is extremely low, nulling will be unnecessary in
most applications.
Single Supply Operation
The LT1077 is fully specified for single supply operation,
(i.e., when the negative supply is 0V). Input common
mode range goes below ground and the output swings
within a few millivolts of ground while sinking current. All
competing micropower op amps either cannot swing to
within 600mV of ground (OP-20, OP-220, OP-420) or
need a pull-down resistor connected to the output to
swing to ground (OP-90, OP-290, OP-490, HA5141/42/
44). This difference is critical because in many applica-
tions these competing devices cannot be operated as
micropower op amps and swing to ground simultaneously.
Consider the difference amplifiers shown in Typical
Applications as an example. When the common mode
signal is high and the output low, the amplifier has to sink
current. In the gain of 10 circuit, the competing devices
require a 30k pull-down resistor at the output to handle the
specified signals. (The LT1077 does not need pull-down
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Common Mode Rejection Ratio
vs Frequency
Power Supply Rejection Ratio
vs Frequency
FREQUENCY (Hz)
10
0
COMMON MODE REJECTION RATIO (dB)
20
40
60
80
100
120
100 1k 10k 100k
LT1077 • TPC28
1M
T
A
= 25°C
V
S
= ±15V
V
S
= 5V, 0V
FREQUENCY (Hz)
0.1
POWER SUPPLY REJECTION RATIO (dB)
80
100
120
100 10k
LT1077 • TPC29
60
40
110
1k 100k
20
0
POSITIVE
SUPPLY
NEGATIVE
SUPPLY
V
S
= ± 2.5V + 1V
P-P
SINE WAVE
T
A
= 25°C
APPLICATIO S I FOR ATIO
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