With a small amount of additional circuitry, the INAx191 can be used in circuits subject to transients that exceed the absolute maximum voltage ratings. The most simple way to protect the inputs from negative transients is to add resistors in series to the IN– and IN+ pins. Use resistors that are 1 kΩ or less, and limit the current in the ESD structures to less than 5 mA. For example, using 1-kΩ resistors in series with the INAx191 allows voltages as low as –5 V, while limiting the ESD current to less than 5 mA. If protection from high-voltage or more-negative, common-voltage transients is needed, use the circuits shown in Figure 8-4 and Figure 8-5. When implementing these circuits, use only Zener diodes or Zener-type transient absorbers (sometimes referred to as transzorbs); any other type of transient absorber has an unacceptable time delay. Start by adding a pair of resistors as a working impedance for the Zener diode, as shown in Figure 8-4. Keep these resistors as small as possible; most often, use around 100 Ω. Larger values can be used with an effect on gain that is discussed in Section 8.1.3. This circuit limits only short-term transients; therefore, many applications are satisfied with a 100-Ω resistor along with conventional Zener diodes of the lowest acceptable power rating. This combination uses the least amount of board space. These diodes can be found in packages as small as SOT-523 or SOD-523.
In the event that low-power Zener diodes do not have sufficient transient absorption capability, a higher-power transzorb must be used. The most package-efficient solution involves using a single transzorb and back-to-back diodes between the device inputs, as shown in Figure 8-5. The most space-efficient solutions are dual, series-connected diodes in a single SOT-523 or SOD-523 package. In either of the examples shown in Figure 8-4 and Figure 8-5, the total board area required by the INA191 with all protective components is less than that of an SO-8 package, and only slightly greater than that of an VSSOP-8 package.
For more information, see Current Shunt Monitor With Transient Robustness Reference Design.