Datasheet
Output Voltage Range
RFI/EMI
Input Filtering
Gain Error % = 100 – 100 ×
5 kΩ
5 kΩ + R
FILT
(
(
(3)
INA193A-Q1 , INA194A-Q1 , INA195A-Q1
INA196A-Q1 , INA197A-Q1 , INA198A-Q1
SBOS366C – AUGUST 2006 – REVISED OCTOBER 2008 ...............................................................................................................................................
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The output of the INA19xA is accurate within the output voltage swing range set by the power supply pin, V+.
This is best illustrated when using the INA195A or INA198A (which are both versions using a gain of 100), where
a 100-mV full-scale input from the shunt resistor requires an output voltage swing of 10 V, and a power-supply
voltage sufficient to achieve 10 V on the output.
Attention to good layout practices is always recommended. Keep traces short and, when possible, use a printed
circuit board (PCB) ground plane with surface-mount components placed as close to the device pins as possible.
Small ceramic capacitors placed directly across amplifier inputs can reduce RFI/EMI sensitivity. PCB layout
should locate the amplifier as far away as possible from RFI sources. Sources can include other components in
the same system as the amplifier itself, such as inductors (particularly switched inductors handling a lot of current
and at high frequencies). RFI can generally be identified as a variation in offset voltage or dc signal levels with
changes in the interfering RF signal. If the amplifier cannot be located away from sources of radiation, shielding
may be needed. Twisting wire input leads makes them more resistant to RF fields. The difference in input pin
location of the INA193A – INA195A versus the INA196A – INA198A may provide different EMI performance.
An obvious and straightforward location for filtering is at the output of the INA19xA series; 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 INA19xA, which is complicated by the internal 5-k Ω ± 30% input impedance (see Figure 5 ).
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:
Total effect on gain error can be calculated by replacing the 5-k Ω term with 5 k Ω – 30% (or 3.5 k Ω ) or
5 k Ω + 30% (or 6.5 k Ω ). 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 1.96%. Worst-case tolerance conditions always
occur at the lower excursion of the internal 5-k Ω resistor (3.5 k Ω ), and the higher excursion of R
FILT
, 3% in this
case.
Note that the specified accuracy of the INA19xA must then be combined in addition to these tolerances. While
this discussion treats accuracy worst-case conditions by combining the extremes of the resistor values, it is
appropriate to use geometric mean or root sum square calculations to total the effects of accuracy variations.
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Product Folder Link(s): INA193A-Q1 INA194A-Q1 INA195A-Q1 INA196A-Q1 INA197A-Q1 INA198A-Q1