• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 46 subscribers
  • Views 766 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

INA195 - Extending Common Mode Beyond +80V

Jim Baker
Prodigy 20 points
Other Parts Discussed in Thread: INA195

I need to measure high side current in a 80V nominal  application. I will need 20V headroom above 80V to accommodate surge overvoltages, power supply tolerances etc. Maximum common mode in this application is 100V.

The INA195 has a maximum common mode of 80V, but the data sheet states that this voltage can be exceeded as long as the current input to any pin is limited to  5mA or less. There is no further guidance I have found on how means to achieve this and how accuracy and bandwidth is affected. Does anyone  know if the common mode can indeed be exceeded on this part and the methods to do so?

Thanks

  • 0
    TI__Expert 4595 points
    Hi Jim,
    It is not recommended to go beyond the maximum rating of the device. Please refer to the "extending common mode range" section in the current monitor FAQ post on the top of this page.
  • 0 in reply to Rabab Itarsiwala
    Prodigy 20 points

    Rabab,

    Thank you for your reply. I am familiar with the techniques described in the reference however they will not work in my application. The techniques all require powering the sense amp off the current shunt voltage using a zener resistor combination. This presents two issues, the first is the minimum voltage in my application is 8V, this mean at 80V I need to drop 75V or so across the resistor which leads to a large power loss, the other more important issues is I am trying to measure short circuit current and supply will collapse very rapidly under these conditions leading to loss of supply to the sense amp. I need to power the sense amp off a separate power supply that will be stable during the short condition which eliminates these sort of techniques.

    In the data sheet for the INA195, the CM range specification has a footnote that explicitly allows the CM range to be exceeded as long as the input current to either pin is kept below 5mA. I presume resistors in-line with the inputs will accomplish this current limiting but need guidance on how to calculate the values to minimize accuracy or speed impacts (or guidance on a method if resistors are not recommended).

  • 0 in reply to Jim Baker
    TI__Expert 4595 points
    Jim,
    Is your common mode range 8 to 100V for this application. What is the supply voltage? What is the minimum and maximum expected load current?
    Also the note that you are referering to is for absolute maximum case. At those conditions the device may not operate per the given specification and operating at the absolute maximum conditions will reduce the life of the devcie and may cause relaibility issues.