INA271-HT datasheet(11/18 Pages) TI

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0.40

0.36

0.32

0.28

0.24

0.20

0.16

0.12

0.08

0.04

(mV)

SENSE

Actual

Ideal

RTI(Referred-To-Input)=

OUT1

- 100mV

OUT1

OUT2

100mV

20mV

INA271-HT

www.ti.com

SBOS521D – SEPTEMBER 2010 – REVISED AUGUST 2013

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

ACCURACY VARIATIONS AS A RESULT OF

VSENSE AND COMMON-MODE VOLTAGE

This region of operation has slightly less accuracy

than Normal Case 1 as a result of the common-mode

The accuracy of the INA271 current shunt monitor is

operating area in which the part functions, as seen in

a function of two main variables: VSENSE (VIN+ – VIN–)

the Output Error vs Common-Mode Voltage curve

and common-mode voltage, VCM, relative to the

(Figure 7). As noted, for this graph VS = 12V; for VCM

supply voltage, VS. VCM is expressed as (VIN+ +

< 12V, the Output Error increases as VCM becomes

VIN–)/2; however, in practice, VCM is seen as the

less than 12V, with a typical maximum error of

voltage at VIN+ because the voltage drop across

0.005% at the most negative VCM = –16V.

VSENSE is usually small.

This section addresses the accuracy of these specific

Low VSENSE Case 1:

operating regions:

VSENSE < 20mV, –16V ≤ VCM < 0; and

Low VSENSE Case 3:

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

VSENSE < 20mV, VS < VCM ≤ 80V

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

Although the INA271 is not designed for accurate

Low VSENSE Case 1:

operation

either

these

regions,

some

VSENSE < 20mV, –16V ≤ VCM < 0

applications are exposed to these conditions. For

Low VSENSE Case 2:

example, when monitoring power supplies that are

VSENSE < 20mV, 0V ≤ VCM ≤ VS

switched on and off while VS is still applied to the

Low VSENSE Case 3:

INA271, it is important to know what the behavior of

the device will be in these regions.

VSENSE < 20mV, VS < VCM ≤ 80V

As VSENSE approaches 0mV, in these VCM regions,

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

the device output accuracy degrades. A larger-than-

normal offset can appear at the current shunt monitor

This

region

operation

provides

the

highest

output with a typical maximum value of VOUT = 60mV

accuracy.

Here,

the

input

offset

voltage

for VSENSE = 0mV. As VSENSE approaches 20mV, VOUT

characterized

and

measured

using

two-step

returns to the expected output value with accuracy as

method. First, the gain is determined by Equation 1.

specified in the Electrical Characteristics. Figure 18

shows this effect (Gain = 20).

(1)

where:

VOUT1 = Output Voltage with VSENSE = 100mV

VOUT2 = Output Voltage with VSENSE = 20mV

Then the offset voltage is measured at VSENSE =

100mV and referred to the input (RTI) of the current

shunt monitor, as shown in Equation 2.

(2)

In the Typical Characteristics, the Output Error vs

Common-Mode Voltage curve (Figure 7) shows the

highest accuracy for the this region of operation. In

this plot, VS = 12V; for VCM ≥ 12V, the output error is

at its minimum. This case is also used to create the

Figure 18. Example for Low VSENSE Cases 1 and 3

VSENSE ≥ 20mV output specifications in the Electrical

(Gain = 20)

Characteristics table.

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