V

RTI(Referred-To-Input)=

OS

V

OUT1

G

- 100mV

G=

V

V

-

OUT1

OUT2

100mV

20mV

-

GainError%=100 -

5kW

5k

+R

W

FILT

100 ´

19

INA200, INA201, INA202

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SBOS374E – NOVEMBER 2006 – REVISED SEPTEMBER 2017

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7.4 Device Functional Modes

7.4.1 Input Filtering

An obvious and straightforward location for filtering is at the output of the INA20x series; however, this location

negates the advantage of the low output impedance of the internal buffer. The only other option for filtering is at

the input pins of the INA20x devices, which is complicated by the internal 5 k

Ω + 30% input impedance. This is

shown in Figure 27. Using the lowest possible resistor values minimizes the initial shift in gain and effects of

tolerance. The effect on initial gain is shown in Equation 1:

(1)

Total effect on gain error can be calculated by replacing the 5-k

Ω term with 5 kΩ – 30%, (or 3.5 kΩ) or 5 kΩ +

30% (or 6.5 k

Ω). The tolerance extremes of RFILT can be inserted into the equation. If a pair of 100-Ω 1%

resistors are used on the inputs, the initial gain error equals 1.96%. Worst-case tolerance conditions always

occur at the lower excursion of the internal 5-k

Ω resistor (3.5 kΩ), and the higher excursion of RFILT – 3% in this

case.

The specified accuracy of the INA20x devices must then be combined in addition to these tolerances. While this

discussion treated accuracy worst-case conditions by combining the extremes of the resistor values, it is

appropriate to use geometric mean or root sum square calculations to total the effects of accuracy variations.

7.4.2 Accuracy Variations as a Result of VSENSE and Common-Mode Voltage

The accuracy of the INA200, INA201, and INA202 current shunt monitors is a function of two main variables:

VSENSE (VIN+ – VIN–), common-mode voltage, (VCM), relative to the supply voltage (VS). VCM is expressed as (VIN+

+ VIN–) / 2; however, in practice, VCM is seen as the voltage at VIN+ because the voltage drop across VSENSE is

typically small.

This section addresses the accuracy of these specific operating regions:

•

Normal Case 1: VSENSE ≥ 20 mV, VCM ≥ VS

•

Normal Case 2: VSENSE ≥ 20 mV, VCM < VS

•

Low VSENSE Case 1: VSENSE < 20 mV, –16 V ≤ VCM < 0

•

Low VSENSE Case 2: VSENSE < 20 mV, 0 V ≤ VCM ≤ VS

•

Low VSENSE Case 3: VSENSE < 20 mV, VS < VCM ≤ 80 V

7.4.2.1 Normal Case 1: VSENSE ≥ 20 mv, VCM ≥ VS

This region of operation provides the highest accuracy. Here, the input offset voltage is characterized and

measured using a two-step method. First, the gain is determined by Equation 2.

where

•

VOUT1 = output voltage with VSENSE = 100 mV

•

VOUT2 = output voltage with VSENSE = 20 mV

(2)

Then the offset voltage is measured at VSENSE = 100 mV, and referred to the input (RTI) of the current shunt

monitor, as shown in Electrical Characteristics: Current-Shunt Monitor.

(3)

In the Typical Characteristics, Figure 7 shows the highest accuracy for the this region of operation. In this plot,

VS = 12 V. For VCM ≥ 12 V, the output error is at the minimum value. This case creates the VSENSE ≥ 20-mV

output specifications in Electrical Characteristics: Current-Shunt Monitor .