INA206 datasheet(12/23 Pages) TI

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INA206

INA207

INA208

SBOS360 − JULY 2006

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

This region of operation has slightly less accuracy than

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

area in which the part functions, as seen in the Output Error

vs Common-Mode Voltage curve. As noted, for this graph

VS = 12V; for VCM < 12V, the Output Error increases as VCM

becomes less than 12V, with a typical maximum error of

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

Low VSENSE Case 1:

VSENSE < 20mV, −16V ≤ VCM < 0;

and Low VSENSE Case 3:

VSENSE < 20mV, VS < VCM ≤ 80V

Although the INA206 family of devices are not designed for

accurate operation in either of these regions, some

applications are exposed to these conditions; for example,

when monitoring power supplies that are switched on and

off while VS is still applied to the INA206, INA207, or

INA208. It is important to know what the behavior of the

devices will be in these regions.

As VSENSE approaches 0mV, in these VCM regions, the

device output accuracy degrades. A larger-than-normal

offset can appear at the current shunt monitor output with

a typical maximum value of VOUT = 300mV for

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

to the expected output value with accuracy as specified in

the Electrical Characteristics. Figure 3 illustrates this

effect using the INA208 (Gain = 100).

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

1012

1416

SENSE (mV)

Actual

Ideal

Figure 3. Example for Low VSENSE Cases 1 and 3

(INA208, Gain = 100)

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

This region of operation is the least accurate for the

INA206 family. To achieve the wide input common-mode

voltage range, these devices use two op amp front ends in

parallel. One op amp front end operates in the positive

input common-mode voltage range, and the other in the

negative input region. For this case, neither of these two

internal amplifiers dominates and overall loop gain is very

low. Within this region, VOUT approaches voltages close to

linear operation levels for Normal Case 2. This deviation

from linear operation becomes greatest the closer VSENSE

approaches 0V. Within this region, as VSENSE approaches

20mV, device operation is closer to that described by

Normal Case 2. Figure 4 illustrates this behavior for the

INA208. The VOUT maximum peak for this case is tested

by maintaining a constant VS, setting VSENSE = 0mV and

sweeping VCM from 0V to VS. The exact VCM at which VOUT

peaks during this test varies from part to part, but the VOUT

maximum peak is tested to be less than the specified VOUT

Tested Limit.

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

SENSE (mV)

INA208 V

OUT Tested Limit

(1)

VCM2

VCM1

CM3

CM4

CM2,VCM3,and VCM4 illustrate the variance

from part to part of the VCM that can cause

maximum V

OUT with VSENSE < 20mV.

OUT Tested Limit at

SENSE =0mV, 0 ≤ VCM1 ≤ VS.

NOTE: (1) INA206 V

OUT Tested Limit = 0.4V. INA207 VOUT Tested Limit = 1V.

Ideal

Figure 4. Example for Low VSENSE Case 2 (INA208,

Gain = 100)

SELECTING RS

The value chosen for the shunt resistor, RS, depends on

the application and is a compromise between small-signal

accuracy and maximum permissible voltage loss in the

measurement line. High values of RS provide better

accuracy at lower currents by minimizing the effects of

offset, while low values of RS minimize voltage loss in the

supply line. For most applications, best performance is

attained with an RS value that provides a full-scale shunt

voltage range of 50mV to 100mV. Maximum input voltage

for accurate measurements is 500mV.

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