Gain Error (%) = 100

(100

Gain Error Factor)

-

´

1000

R

+ 1000

S

1000

R

+ 1000

S

10,000

(9

R

+ 10,000

´

10,000

(9

R

+ 10,000

´

20,000

(17

R

+ 20,000

´

20,000

(17

R

+ 20,000

´

Gain Error Factor =

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

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:

(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

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 10

Ω 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 10

Ω series resistors.

Using an INA199A1 or INA199B1 with the same 10

Ω 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.

Copyright © 2009–2012, Texas Instruments Incorporated

Submit Documentation Feedback

11

Product Folder Links: INA199A1 INA199B1 INA199A2 INA199B2 INA199A3 INA199B3