Datasheet

G=1+
49.4kW
R
G
INA826
SBOS562E –AUGUST 2011–REVISED APRIL 2013 www.ti.com
SETTING THE GAIN
Gain of the INA826 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 49.4-kΩ term in Equation 1 comes from the
sum of the two internal 24.7-kΩ feedback resistors. These 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 INA826.
Table 1. Commonly-Used Gains and Resistor Values
DESIRED GAIN (V/V) R
G
(Ω) NEAREST 1% R
G
(Ω)
1 — —
2 49.4k 49.9k
5 12.35k 12.4k
10 5.489k 5.49k
20 2.600k 2.61k
50 1.008k 1k
100 499 499
200 248 249
500 99 100
1000 49.5 49.9
Gain Drift
The stability and temperature drift of the external gain setting resistor, R
G
, also affects gain. The contribution of
R
G
to gain accuracy and drift can be directly inferred from the gain of Equation 1.
The best gain drift of 1 ppm/℃ can be achieved when the INA826 uses G = 1 without R
G
connected. In this case,
the gain drift is limited only by the slight mismatch of the temperature coefficient of the integrated 50-kΩ resistors
in the differential amplifier (A
3
). At G greater than 1, the gain drift increases as a result of the individual drift of the
24.7-kΩ resistors in the feedback of A
1
and A
2
, relative to the drift of the external gain resistor R
G
. Process
improvements of the temperature coefficient of the feedback resistors now make it possible to specify a
maximum gain drift of the feedback resistors of 35 ppm/℃, thus significantly improving the overall temperature
stability of applications using gains greater than 1.
Low resistor values required for high gain can make wiring resistance important. Sockets add to the wiring
resistance and contribute additional gain error (such as a possible unstable gain error) at gains of approximately
100 or greater. To ensure stability, avoid parasitic capacitance of more than a few picofarads at R
G
connections.
Careful matching of any parasitics on both R
G
pins maintains optimal CMRR over frequency; see Typical
Characteristics curves (Figure 19 and Figure 20).
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