LT6010
10
sn6010 6010fs
Preserving Input Precision
Preserving the input accuracy of the LT6010 requires that
the applications circuit and PC board layout do not intro-
duce errors comparable to or greater than the 20µV typical
offset of the amplifier. Temperature differentials across
the input connections can generate thermocouple volt-
ages 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) allow
high accuracy to be maintained with high impedance
sources and feedback resistors. The LT6010 low input
bias currents are obtained by a cancellation circuit on-
chip. The input bias currents are permanently trimmed at
wafer testing to a low level. 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
LT6010’s input bias current. For example, 10GΩ of leak-
age between a 15V supply lead and an input lead will gen-
erate 1.5nA! Surround the input leads by a guard ring, driven
to the same potential as the input common mode, to avoid
excessive leakage in high impedance applications.
Input Protection
The LT6010 features on-chip back-to-back diodes be-
tween the input devices, along with 500Ω resistors in
series with either input. This internal protection limits the
input current to approximately 10mA (the maximum
allowed) 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 LT6010 output is able to swing nearly 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 LT6010 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 with a
minimum noise of 14nV/√Hz for very low source imped-
ance. If the source impedance is more than 1MΩ, the input
current noise of the amplifier, multiplied by this high
impedance, starts to contribute and eventually dominate.
Total input noise spectral density can be calculated as:
v e kTR i R
n TOTAL n S n S()
()=+ +
2
2
4
where e
n
= 14nV/√Hz, i
n
= 0.1pA/√Hz and R
S
the total
impedance at the input, including the source impedance.
APPLICATIO S I FOR ATIO
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