INA194AIDBVTG4 Datasheet, PDF (11/24 Pages) Texas Instruments – CURRENT SHUNT MONITOR −16V to +80V Common-Mode Range

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RFI/EMI
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
INA193-INA195 versus the INA196-INA198 may
provide different EMI performance.
INPUT FILTERING
An obvious and straightforward location for filtering is
at the output of the INA193-INA198; 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
INA193-INA198, which is complicated by the internal
5kΩ + 30% input impedance; this is illustrated in
Figure 22. 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 3:
GainError% = 100 -
5kW
5kW + R_FILT
´ 100
(3)
Total effect on gain error can be calculated by
replacing the 5kΩ term with 5kΩ − 30%, (or 3.5kΩ) or
5kΩ + 30% (or 6.5kΩ). The tolerance extremes of
R_FILT can also be inserted into the equation. If a pair
of 100Ω 1% resistors are used on the inputs, the
initial gain error will be approximately 2%. Worst-case
tolerance conditions will always occur at the lower
excursion of the internal 5kΩ resistor (3.5kΩ), and the
higher excursion of R_FILT − 3% in this case.
INA193, INA194
INA195, INA196
INA197, INA198
SBOS307F – MAY 2004 – REVISED FEBRUARY 2010
Note that the specified accuracy of the
INA193-INA198 must then be combined in addition to
these tolerances. While this discussion treated
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.
V_SUPPLY
R_SHUNT << R_FILTER
LOAD
R_FILT < 100W
C_FILT
VIN+
R_FILT < 100W
f-3dB =
f_-3dB
1
2p (2 R_FILT) C_FILT
+5V
VIN-
V+
R₁
R₁
5kW
5kW
INA193-INA198 ^RL
OUT
Figure 22. Input Filter (Gain Error − 1.5% to
−2.2%)
Copyright © 2004–2010, Texas Instruments Incorporated
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