GainError% + 100 * 100

5k W

5k W ) RFILT

INA193A-EP

SBOS400A – MAY 2007 – REVISED SEPTEMBER 2013

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Output Voltage Range

The output of the INA193A 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.

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.

Input Filtering

An obvious and straightforward location for filtering is at the output of the INA193A; 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 INA193A, which is complicated by the internal 5-k

Ω + 30% input impedance; this is

illustrated in 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:

(3)

Total effect on gain error can be calculated by replacing the 5-k

Ω term with 5 kΩ – 30%, (or 3.5 kΩ) or

5 k

Ω + 30% (or 6.5 kΩ). The tolerance extremes of RFILT can also be inserted into the equation. If a pair of 100-Ω

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 5-k

Ω resistor (3.5 kΩ), and the higher excursion

of RFILT – 3% in this case. Note that the specified accuracy of the INA193A 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.

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