10.1 Common-Mode Transients Greater Than 26 V

With a small amount of additional circuitry, the INAx181 can be used in circuits subject to transients higher than 26 V, such as automotive applications. 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; see Figure 55. Keep these resistors as small as possible; most often, around 10 Ω. Larger values can be used with an effect on gain that is discussed in the Signal Filteringsection. This circuit limits only short-term transients; therefore, many applications are satisfied with a 10-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.

Figure 55. Transient Protection Using Dual Zener Diodes

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 56. 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 55 and Figure 56, the total board area required by the INAx181 with all protective components is less than that of an SO-8 package, and only slightly greater than that of an MSOP-8 package.

Figure 56. Transient Protection Using a Single Transzorb and Input Clamps

For more information, see Current Shunt Monitor With Transient Robustness Reference Design.