INA200 datasheet(17/33 Pages) TI1

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RTI(Referred-To-Input)=

OUT1

- 100mV

OUT1

OUT2

100mV

20mV

GainError%=100 -

5kW

FILT

100 ´

INA200, INA201, INA202

www.ti.com

SBOS374D – NOVEMBER 2006 – REVISED OCTOBER 2015

7.4 Device Functional Modes

7.4.1 Input Filtering

An obvious and straightforward location for filtering is at the output of the INA200, INA201, and INA202 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 INA200, INA201, and INA202 devices, which is complicated by the

internal 5 k

Ω + 30% input impedance; this is illustrated in Figure 27. Using the lowest possible resistor values

minimizes both the initial shift in gain and effects of tolerance. The effect on initial gain is given by 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 also be inserted into the equation. If a pair of 100 Ω 1%

resistors are used on the inputs, the initial gain error will be 1.96%. Worst-case tolerance conditions will 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 INA200, INA201, and INA202 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–) and 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 usually 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 curve 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 its minimum. This case is also used to create the VSENSE ≥

20-mV output specifications in Electrical Characteristics: Current-Shunt Monitor .

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