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Low V
SENSE
Case 2: V
SENSE
< 20mV, 0V ≤ V
CM
≤ V
S
Normal Case 2: V
SENSE
≥ 20mV, V
CM
< V
S
Low V
SENSE
Case 1:
NOTE:(1)INA206V TestedLimit=0.4V.
OUT
INA207V TestedLimit=1V.
OUT
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0
2
V (V)
OUT
V (mV)
SENSE
24
Ideal
INA208V TestedLimit
OUT
(1)
V TestedLimitat
0mV,0
OUT
V = V V .
SENSE CM1 S
££
V , ,and illustratethevariance
fromparttopartofthe thatcancause
maximum with
CM2
V V
V
V V <20mV.
CM3 CM4
CM
OUT SENSE
V
CM2
V
CM1
V
CM3
V
CM4
6 8 10
12 14
16 18 20
22
4
SELECTING R
S
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0
2
V (V)
OUT
V (mV)
SENSE
20
Actual
Ideal
4
6 8 10
12 14
16 18
INA206
INA207
INA208
SBOS360E – JUNE 2006 – REVISED OCTOBER 2007
In the Typical Characteristics, the Output Error vs
Common-Mode Voltage curve shows the highest
This region of operation is the least accurate for the
accuracy for the this region of operation. In this plot,
INA206 family. To achieve the wide input
V
S
= 12V; for V
CM
≥ 12V, the output error is at its
common-mode voltage range, these devices use two
minimum. This case is also used to create the V
SENSE
op amp front ends in parallel. One op amp front end
≥ 20mV output specifications in the Electrical
operates in the positive input common-mode voltage
Characteristics table.
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, V
OUT
approaches voltages close to linear
This region of operation has slightly less accuracy
operation levels for Normal Case 2. This deviation
than Normal Case 1 as a result of the common-mode
from linear operation becomes greatest the closer
operating area in which the part functions, as seen in
V
SENSE
approaches 0V. Within this region, as V
SENSE
the Output Error vs Common-Mode Voltage curve. As
approaches 20mV, device operation is closer to that
noted, for this graph V
S
= 12V; for V
CM
< 12V, the
described by Normal Case 2. Figure 32 illustrates this
Output Error increases as V
CM
becomes less than
behavior for the INA208. The V
OUT
maximum peak for
12V, with a typical maximum error of 0.005% at the
this case is tested by maintaining a constant V
S
,
most negative V
CM
= – 16V.
setting V
SENSE
= 0mV and sweeping V
CM
from 0V to
V
S
. The exact V
CM
at which V
OUT
peaks during this
test varies from part to part, but the V
OUT
maximum
V
SENSE
< 20mV, – 16V ≤ V
CM
< 0; and
peak is tested to be less than the specified V
OUT
Low V
SENSE
Case 3:
Tested Limit.
V
SENSE
< 20mV, V
S
< V
CM
≤ 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 V
S
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 V
SENSE
approaches 0mV, in these V
CM
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 V
OUT
= 300mV for V
SENSE
= 0mV. As V
SENSE
approaches 20mV, V
OUT
returns to the expected
output value with accuracy as specified in the
Electrical Characteristics. Figure 31 illustrates this
effect using the INA208 (Gain = 100).
Figure 32. Example for Low V
SENSE
Case 2
(INA208, Gain = 100)
The value chosen for the shunt resistor, R
S
, depends
on the application and is a compromise between
small-signal accuracy and maximum permissible
voltage loss in the measurement line. High values of
R
S
provide better accuracy at lower currents by
minimizing the effects of offset, while low values of
R
S
minimize voltage loss in the supply line. For most
applications, best performance is attained with an R
S
value that provides a full-scale shunt voltage range of
50mV to 100mV. Maximum input voltage for accurate
measurements is (V
S
– 0.2)/Gain.
Figure 31. Example for Low V
SENSE
Cases 1 and 3
(INA208, Gain = 100)
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