Datasheet

5 +
80 kW
R
G
INA827
SBOS631A –JUNE 2012–REVISED JULY 2013 www.ti.com
SETTING THE GAIN
Device gain is set by a single external resistor (R
G
), connected between pins 2 and 3. The value of R
G
is
selected according to Equation 1:
(1)
Table 1 lists several commonly-used gains and resistor values. The on-chip resistors are laser-trimmed to
accurate absolute values. The accuracy and temperature coefficients of these resistors are included in the gain
accuracy and drift specifications of the INA827.
Table 1. Commonly-Used Gains and Resistor Values
DESIRED GAIN (V/V) R
G
(Ω) NEAREST 1% R
G
(Ω)
5 — —
10 16.00k 15.8k
20 5.333k 5.36k
50 1.778k 1.78k
100 842.1 845
200 410.3 412
500 161.6 162
1000 80.40 80.6
Gain Drift
The stability and temperature drift of the external gain setting resistor (R
G
) also affects gain. The R
G
contribution
to gain accuracy and drift can be directly inferred from the gain of Equation 1.
The best gain drift of 1 ppm per degree Celsius can be achieved when the INA827 uses G = 5 without R
G
connected. In this case, the gain drift is limited only by the slight temperature coefficient mismatch of the
integrated 50-kΩ resistors in the differential amplifier (A
3
). At gains greater than 5, the gain drift increases as a
result of the individual drift of the resistors in the feedback of A
1
and A
2
, relative to the drift of the external gain
resistor R
G
. Process improvements to the temperature coefficient of the feedback resistors now enable a
maximum gain drift of the feedback resistors to be specified at 35 ppm per degree Celsius, thus significantly
improving the overall temperature stability of applications using gains greater than 5.
Low resistor values required for high gains can make wiring resistance important. Sockets add to wiring
resistance and contribute additional gain error (such as possible unstable gain errors) at gains of approximately
100 or greater. To ensure stability, avoid parasitic capacitances greater than a few picofarads at R
G
connections.
Careful matching of any parasitics on both R
G
pins maintains optimal CMRR over frequency; see the Typical
Characteristics.
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