INA270_07 BURR-BROWN [Burr-Brown Corporation], INA270_07 Datasheet - Page 10

• Manufacturer Part Number: INA270_07
• Description: Voltage Output, Unidirectional Measurement Current-Shunt Monitor
• Manufacturer: BURR-BROWN [Burr-Brown Corporation]

INA270
INA271
SBOS381A – FEBRUARY 2007 – REVISED APRIL 2007
10
ACCURACY VARIATIONS AS A RESULT OF
V
The accuracy of the INA270 and INA271 current
shunt monitors is a function of two main variables:
V
V
expressed as (V
V
voltage drop across V
This section addresses the accuracy of these
specific operating regions:
Normal Case 1: V
This region of operation provides the highest
accuracy.
characterized and measured using a two-step
method. First, the gain is determined by
where:
Then the offset voltage is measured at V
100mV and referred to the input (RTI) of the current
shunt monitor, as shown in
In the
Common-Mode Voltage curve
highest accuracy for the this region of operation. In
this plot, V
at its minimum. This case is also used to create the
V
Characteristics
G =
V RTI (Referred-To-Input) =
SENSE
CM
CM
OS
SENSE
SENSE
, relative to the supply voltage, V
Normal Case 1: V
Normal Case 2: V
Low V
Low V
Low V
V
V
100mV
is seen as the voltage at V
OUT1
OUT2
V
OUT1
Typical
AND COMMON-MODE VOLTAGE
V
V
V
(V
SENSE
SENSE
SENSE
20mV output specifications in the
SENSE
SENSE
SENSE
= Output Voltage with V
= Output Voltage with V
IN+
S
-
Here,
-
= 12V; for V
V
20mV
– V
OUT2
< 20mV, –16V
< 20mV, 0V
< 20mV, V
table.
Characteristics, the Output Error vs
Case 1:
Case 2:
Case 3:
IN+
SENSE
IN–
the
+ V
) and common-mode voltage,
SENSE
SENSE
SENSE
CM
IN–
input
S
20mV, V
)/2; however, in practice,
Equation
is usually small.
< V
20mV, V
20mV, V
12V, the output error is
V
V
CM
CM
(Figure
V
OUT1
G
offset
CM
SENSE
SENSE
CM
IN+
80V
V
< 0
2.
S
CM
CM
- 100mV
6) shows the
because the
V
= 100mV
= 20mV
Equation
< V
S
voltage
S
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V
. V
Electrical
S
S
SENSE
CM
1.
(1)
(2)
is
is
=
Normal Case 2: V
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
(Figure
< 12V, the Output Error increases as V
less than 12V, with a typical maximum error of
0.005% at the most negative V
Low
V
Low
V
Although the INA270 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
applied to the INA270 or INA271, it is important to
know what the behavior of the devices will be in
these regions.
As V
the
larger-than-normal offset can appear at the current
shunt monitor output with a typical maximum value of
V
approaches 20mV, V
output value with accuracy as specified in the
Electrical
using the INA271 (Gain = 20).
Figure 17. Example for Low V
SENSE
SENSE
OUT
SENSE
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
device
0
= 60mV for V
< 20mV, V
V
6). As noted, for this graph V
V
0
< 20mV, –16V
SENSE
SENSE
Characteristics.
approaches 0mV, in these V
2
output
(INA271, Gain = 20)
4
Case
Case
S
SENSE
Actual
< V
6
OUT
CM
SENSE
8
V
accuracy
Figure 17
3:
SENSE
20mV, V
1:
returns to the expected
80V
10
V
(mV)
Ideal
CM
CM
= 0mV. As V
SENSE
12
= –16V.
CM
< 0; and
shows this effect
S
14
Cases 1 and 3
< V
degrades.
= 12V; for V
CM
16
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CM
S
becomes
18
regions,
S
is still
SENSE
20
CM
A