Gain Error (%) = 100

(100

Gain Error Factor)

-

´

S

2500

3 R

2500

u

S

1000

R

1000

S

12,500

11 R

12,500

u

Gain Error Factor =

(1250 ´ INT

R

)

(1250

S

´

´

´

R ) + (1250

R

) + (R

R

)

INT

S

INT

27

INA302, INA303

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SBOS775C – SEPTEMBER 2016 – REVISED MARCH 2019

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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 RINT as illustrated in Figure 50). 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 measured at

the device input pins is given in Equation 5:

where

•

RINT is the internal input resistor (R3 and R4).

•

RS is the external series resistance.

(5)

With the adjustment factor from Equation 5, including the device internal input resistance, this factor varies with

each gain version, as shown in Table 3. Each individual device gain error factor is shown in Table 4.

Table 3. Input Resistance

PRODUCT

GAIN

RINT (kΩ)

INA30xA1

20

12.5

INA30xA2

50

5

INA30xA3

100

2.5

Table 4. Device Gain Error Factor

PRODUCT

SIMPLIFIED GAIN ERROR FACTOR

INA30xA1

INA30xA2

INA30xA3

The gain error that is expected from the addition of the external series resistors is then calculated based on

Equation 6:

(6)

For example, using an INA302A2 and the corresponding gain error equation from Table 4, a series resistance of

10 Ω results in a gain error factor of 0.99. The corresponding gain error is then calculated using Equation 6,

resulting in a gain error of approximately 1% solely because of the external 10-Ω series resistors.