Datasheet
GainError%=100 [100 {R/(R+R )}]-
FILT
´
f
-3
dB
=
f
-3dB
1
2π
(
2 R ) C
FILTER FILTER
LOAD
V
SUPPLY
R
SHUNT
<< R
FILTER
R < 10 Ω
FILTER
C
FILTER
R < 10 Ω
FILTER
V+
OUT
Output
GND
IN-
IN+
INA21x-Q1
Reference
Voltage
C
BYPASS
0.01 µF
to
0.1 µF
2.7 V to 26 V
REF
R
1
R
3
R
2
R
4
INA212-Q1, INA213A-Q1
INA214-Q1
www.ti.com
SBOS475D –MARCH 2009–REVISED OCTOBER 2013
A less frequent case of unipolar output biasing is to bias the output by connecting the REF pin to the supply; in
this case, the quiescent output for zero input is at quiescent supply. This configuration would only respond to
negative currents (inverted voltage polarity at the device input).
BIDIRECTIONAL OPERATION
Bidirectional operation allows the INA21x-Q1 to measure currents through a resistive shunt in two directions. In
this case, the output can be set anywhere within the limits of what the reference inputs allow (that is, between 0
V and V+). Typically, it is set at half-scale for equal range in both directions. In some cases, however, it is set at
a voltage other than half-scale when the bidirectional current is nonsymmetrical.
The quiescent output voltage is set by applying voltage to the reference input. Under zero differential input
conditions the output assumes the same voltage as is applied to the reference input.
INPUT FILTERING
An obvious and straightforward location for filtering is at the output of the INA21x-Q1; 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 INA21x-Q1; this location requires consideration of the ±30% tolerance of the input
impedance. Figure 24 shows a filter placed at the input pins.
Figure 24. Input Filter
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)
Where R is the value for R
3
or R
4
from Table 1 for the model in question.
Table 1.
PRODUCT GAIN (V/V) R
3
AND R
4
INA212-Q1 1000 1 kΩ
INA213A-Q1 50 20 kΩ
INA214-Q1 100 10 kΩ
Using an INA212-Q1, for example, the total effect on gain error can be calculated by replacing the R with
1 kΩ – 30%, (or 700 Ω) or 1 kΩ + 30% (or 1.3 kΩ). The tolerance extremes of R
FILT
can also be inserted into the
equation. If a pair of 100-Ω 1% resistors are used on the inputs, the initial gain error is approximately 2%.
Copyright © 2009–2013, Texas Instruments Incorporated Submit Documentation Feedback 9
Product Folder Links: INA212-Q1 INA213A-Q1 INA214-Q1