Datasheet

Error_R =
FILTER
? 100
(I I ) R
V
-
FILTER
SHUNT
IN+ IN-
?
V
OUT
IN-
IN+
GND
R
SHUNT
C
FILTER
INA216
Load
V
CM
R
10
FILTER
W?
R
10
FILTER
W?
V
OUT
IN-
IN+
GND
R
SHUNT
INA216
Load
V
CM
R
10W
PROTECT
?
R
10W
PROTECT
?
Z
2
Z
1
INA216
SBOS503C –JUNE 2010–REVISED NOVEMBER 2011 www.ti.com
Input Filtering driving any current). Connecting a 100kΩ load to the
4V output now increases the current by an additional
An ideal location where filtering is implemented is at
40μA. This increase in current flowing through the
the inputs for a device. Placing an input filter in front
IN+ pin would change the additional gain error from
of the INA216, though, is not recommended but can
0.3% to 1.3%.
be implemented if it is determined to be necessary.
This location is not recommended for filtering If filtering is required for the application and the gain
because adding input filters induces an additional error introduced by the input filter resistors exceeds
gain error to the device that can easily exceed the the available error budget for this circuit, a filter can
device maximum gain error specification of 0.2%. In be implemented following the INA216. Placing a filter
the INA216, the nominal current into the IN+ pin is in at the output of the current shunt monitor is not
the range of 13μA while the bias current into the IN– typically the ideal location because the benefit of the
pin is in the range of approximately 3μA. The current low impedance output of the amplifier is lost.
flowing into the IN+ pin includes both the input bias Applications that require the low impedance output
current as well as the quiescent current. Where the require an additional buffer amplifier that follows the
issue of input filtering begins to become more of an post current shunt monitor filter.
issue is that as the quiescent current of the INA216
also flows through the IN+ pin, when the output
Using the INA216 With Transients Above 5.5V
begins to drive current, this additional current also
With a small amount of additional circuitry, INA216
flows through the IN+ pin, creating an even larger
can be used in circuits subject to transients higher
error.
than 5.5V. Use only zener diode or zener-type
Placing a typical common-mode filter of 10Ω in series
transient absorbers, which are sometimes referred to
with each input and a 0.1μF capacitor across the
as Transzorbs. Any other type of transient absorber
input pins, as shown in Figure 21, introduces an
has an unacceptable time delay. To use these
additional gain error into the system. For example,
protection devices, resistors are required in series
consider an application using the INA216A3 with a
with the INA216 inputs, as shown in Figure 22. These
full-scale output of 4V, assuming that the device is
resistors serve as a working impedance for the zener.
not driving any output current. The shunt voltage
It is desirable to keep these resistors as small as
needed to create the 4V output with a gain of 100 is
possible because of the error described in the Input
40mV. With 10Ω filter resistors on each input, there is
Filtering section. These protection resistors are most
a difference voltage created that subtracts from the
often around 10Ω. Larger values can be used with a
40mV full-scale differential current. The error can be
greater impact to the total gain error. Because this
calculated using Equation 2.
circuit limits only short-term transients, many
applications are satisfied with a 10Ω resistor along
with conventional zener diodes of the lowest power
(2)
rating that can be found. This combination uses the
least amount of board space. These diodes can be
found in packages as small as SOT-523 or SOD-523.
The use of these protection components may allow
the INA216 to survive from being damaged in
environments where large transients are common.
Figure 21. Input Filter
As mentioned previously, the current flowing into the
IN+ pin increases once the output begins to drive
current because of the quiescent current also flowing
Figure 22. Transient Protection Using Dual Zener
into the IN+ pin. The previous example resulted in an
Diodes
additional gain error of 0.3% as a result of the 10Ω
filter resistors (assuming the output stage was not
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