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INA 196, adding input protection.

Jon George
Prodigy 10 points
Other Parts Discussed in Thread: INA196

Sorry for my lack of experience with these but I have a situation where the INA196 is being damaged. I haven't been able to observe the fail but I suspect transients due to switching between two power sources that are monitored by this device. The INA196 is measuring across a 1 ohm resistor in series with a load and is supplied by switching between one of two batteries. The battery input is less than about 32V and the load is a DC to DC power supply and the grounds are all connected. The currents will be about 0.5A or less. The datasheet indicates to add zeners or transzorbs to the input but I'm unsure how they should be connected. I'm thinking about opposing zeners connected to Vin+ to ground to protect + and - voltages, the positive protection zener is 39V and the negative oriented zener is 12V. I'm worried that this configuration would expose the zeners to too much current and they too will fail. Any advice is welcome.

  • 0
    TI__Expert 6930 points

    Hi Jon,

    I am sorry that you are experiencing troubles with the INA196.  From your description it sounds like voltages may be jumping around during the switchover.  Nothing you mentioned yet gives me concern that you have possibly violated the maximum common mode volatge of 80V, but I think we should start by identifying the limits of the device. 

    The common mode voltage (Vin+ and Vin-) must always be within -16V to 80V.  Do you think it is possible that your common mode voltage is jumping outside of this range? 

    The maximum input differential voltage allowed between the input pins is required to be between -18V and 18V...do you think there is any chance that somehow a very large differential voltage may be ocurring during the switchover? 

    I did not see what power supply voltage you are applying to the Vs pin...to prevent damage, this pin must be kept between -0.3V and 18V...do you think it is possible that the power supply to the Vs pin on the INA is jumping outside of this range?  The method you described sounds like a protection strategy to protect against common mode voltage transients...your idea sounds correct and you can place a small resitance <100 Ohms in series with the Zeners.  This 100 Ohms will have an impact on gain accuracy which is described on page 11 of the data sheet in the filtering section.  Just make sure that whatever resistance is placed on one input that you place the same amount of resistance on the other input.  If you would like to provide a schematic so I can better assist you you may contact me directly by email so as not to share your schematic on the forum.  My email is mullins_ed@ti.com

    Are you destroying 100% of the parts or just random parts?  Would you like instructions on how to return a failed device to TI for failure analysis?