Datasheet

Gain Error (%) = 100 (100 Gain Error Factor)- ´
1000
R + 1000
S
1000
R + 1000
S
10,000
(9 R + 10,000´
S
)
10,000
(9 R + 10,000´
S
)
20,000
(17 R + 20,000´
S
)
20,000
(17 R + 20,000´
S
)
Gain Error Factor =
(1250 ´
INT
R )
(1250
S
´ ´ ´R ) + (1250 R ) + (R R )
INT S INT
INA199A1, INA199B1
INA199A2, INA199B2
INA199A3, INA199B3
www.ti.com SBOS469D –MAY 2009–REVISED NOVEMBER 2012
The amount of variance in the differential voltage present at the device input relative to the voltage developed at
the shunt resistor is based both on the external series resistance value as well as the internal input resistors, R3
and R4 (or R
INT
as shown in Figure 21). The reduction of the shunt voltage reaching the device input pins
appears as a gain error when comparing the output voltage relative to the voltage across the shunt resistor. A
factor can be calculated to determine the amount of gain error that is introduced by the addition of external series
resistance. The equation used to calculate the expected deviation from the shunt voltage to what is seen at the
device input pins is given in Equation 1:
where:
R
INT
is the internal input resistor (R3 and R4), and
R
S
is the external series resistance. (1)
With the adjustment factor equation including the device internal input resistance, this factor varies with each
gain version, as shown in Table 1. Each individual device gain error factor is shown in Table 2.
Table 1. Input Resistance
PRODUCT GAIN R
INT
(kΩ)
INA199A1 50 20
INA199B1 50 20
INA199A2 100 10
INA199B2 100 10
INA199A3 200 5
INA199B3 200 5
Table 2. Device Gain Error Factor
PRODUCT SIMPLIFIED GAIN ERROR FACTOR
INA199A1
INA199B1
INA199A2
INA199B2
INA199A3
INA199B3
The gain error that can be expected from the addition of the external series resistors can then be calculated
based on Equation 2:
(2)
For example, using an INA199A2 or INA199B2 and the corresponding gain error equation from Table 2, a series
resistance of 10Ω results in a gain error factor of 0.991. The corresponding gain error is then calculated using
Equation 2, resulting in a gain error of approximately 0.89% solely because of the external 10Ω series resistors.
Using an INA199A1 or INA199B1 with the same 10Ω series resistor results in a gain error factor of 0.991 and a
gain error of 0.84% again solely because of these external resistors.
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Product Folder Links: INA199A1 INA199B1 INA199A2 INA199B2 INA199A3 INA199B3