LT6011/LT6012
11
60112fc
Typical perForMance characTerisTics
Small-Signal Transient Response
Large-Signal Transient Response Rail-to-Rail Output Swing
20mV/DIV
2µs/DIV
6011 G28A
V
= 1
2V/DIV 0V
50µs/DIV
6011 G29A
V
= –1
V
S
= ±15V
1V/DIV
5V
0V
100µs/DIV
6011 G30A
V
= –1
V
S
= 5V, 0V
applicaTions inForMaTion
Preserving Input Precision
Preserving the input accuracy of the LT6011/LT6012 re-
quires that the applications circuit and PC board layout do
not introduce errors comparable to or greater than the 25µV
typical offset of the amplifiers. Temperature differentials
across the input connections can generate thermocouple
voltages of 10’s of microvolts so the connections to the
input leads should be short, close together and away from
heat dissipating components. Air currents across the board
can also generate temperature differentials.
The extremely low input bias currents (20pA typical) al-
low high accuracy to be maintained with high impedance
sources and feedback resistors. The LT6011/LT6012 low
input bias currents are obtained by a cancellation circuit
on-chip. This causes the resulting I
B
+
and I
B
–
to be uncor-
related, as implied by the I
OS
specification being comparable
to I
B
. Do not try to balance the input resistances in each
input lead; instead keep the resistance at either input as
low as possible for maximum accuracy.
Leakage currents on the PC board can be higher than the
input bias current. For example, 10GΩ of leakage between
a 15V supply lead and an input lead will generate 1.5nA!
Surround the input leads with a guard ring driven to the
same potential as the input common mode to avoid exces-
sive leakage in high impedance applications.
Input Protection
The LT6011/LT6012 feature on-chip back-to-back diodes
between the input devices, along with 500Ω resistors in
series with either input. This internal protection limits the
input current to approximately 10mA (the maximum al-
lowed) for a 10V differential input voltage. Use additional
external series resistors to limit the input current to 10mA
in applications where differential inputs of more than 10V
are expected. For example, a 1k resistor in series with each
input provides protection against 30V differential voltage.
Input Common Mode Range
The LT6011/LT6012 output is able to swing close to each
power supply rail (rail-to-rail out), but the input stage
is limited to operating between V
–
+ 1V and V
+
– 1.2V.
Exceeding this common mode range will cause the gain
to drop to zero, however, no phase reversal will occur.
Total Input Noise
The LT6011/LT6012 amplifier contributes negligible noise
to the system when driven by sensors (sources) with
impedance between 20kΩ and 1MΩ. Throughout this
range, total input noise is dominated by the 4kTR
S
noise
of the source. If the source impedance is less than 20kΩ,
the input voltage noise of the amplifier starts to contribute
